feat(gateway): add web search emulation for Anthropic API Key accounts

Inject web search capability for Claude Console (API Key) accounts that
don't natively support Anthropic's web_search tool. When a pure
web_search request is detected, the gateway calls Brave Search or Tavily
API directly and constructs an Anthropic-protocol-compliant SSE/JSON
response without forwarding to upstream.

Backend:
- New `pkg/websearch/` SDK: Brave and Tavily provider implementations
  with io.LimitReader, proxy support, and Redis-based quota tracking
  (Lua atomic INCR + TTL, DECR rollback on failure)
- Global config via `settings.web_search_emulation_config` (JSON) with
  in-process cache + singleflight, input validation, API key merge on
  save, and sanitized API responses
- Channel-level toggle via `channels.features_config` JSONB column
  (DB migration 101)
- Account-level toggle via `accounts.extra.web_search_emulation`
- Request interception in `Forward()` with SSE streaming response
  construction using json.Marshal (no manual string concatenation)
- Manager hot-reload: `RebuildWebSearchManager()` called on config save
  and startup via `SetWebSearchRedisClient()`
- 70 unit tests covering providers, manager, config validation,
  sanitization, tool detection, query extraction, and response building

Frontend:
- Settings → Gateway tab: Web Search Emulation config card with global
  toggle, provider list (add/remove, API key, priority, quota, proxy)
- Channels → Anthropic tab: web search emulation toggle with global
  state linkage (disabled when global off)
- Account Create/Edit modals: web search emulation toggle for API Key
  type with Toggle component
- Full i18n coverage (zh + en)

frontend/src/views/admin/ChannelsView.vue

@@ -306,6 +306,24 @@
               </div>
             </div>
 
+            <!-- Web Search Emulation (Anthropic only) -->
+            <div v-if="section.platform === 'anthropic'" class="border-t border-gray-200 pt-3 dark:border-dark-600">
+              <div class="flex items-center justify-between">
+                <div>
+                  <label class="text-xs font-medium text-orange-600 dark:text-orange-400">
+                    {{ t('admin.channels.form.webSearchEmulation') }}
+                  </label>
+                  <p v-if="webSearchGlobalEnabled" class="mt-0.5 text-[11px] text-amber-500 dark:text-amber-400">
+                    {{ t('admin.channels.form.webSearchEmulationHint') }}
+                  </p>
+                  <p v-else class="mt-0.5 text-[11px] text-gray-400">
+                    {{ t('admin.channels.form.webSearchEmulationGlobalDisabled') }}
+                  </p>
+                </div>
+                <Toggle v-model="section.web_search_emulation" :disabled="!webSearchGlobalEnabled" />
+              </div>
+            </div>
+
             <!-- Model Mapping -->
             <div>
               <div class="mb-1 flex items-center justify-between">
@@ -423,6 +441,7 @@
 import { ref, reactive, computed, onMounted, onUnmounted } from 'vue'
 import { useI18n } from 'vue-i18n'
 import { useAppStore } from '@/stores/app'
+import { extractApiErrorMessage } from '@/utils/apiError'
 import { adminAPI } from '@/api/admin'
 import type { Channel, ChannelModelPricing, CreateChannelRequest, UpdateChannelRequest } from '@/api/admin/channels'
 import type { PricingFormEntry } from '@/components/admin/channel/types'
@@ -446,6 +465,18 @@ import { getPersistedPageSize } from '@/composables/usePersistedPageSize'
 const { t } = useI18n()
 const appStore = useAppStore()
 
+// Web Search global enabled state (loaded once on mount)
+const webSearchGlobalEnabled = ref(false)
+async function loadWebSearchGlobalState() {
+  try {
+    const cfg = await adminAPI.settings.getWebSearchEmulationConfig()
+    webSearchGlobalEnabled.value = cfg?.enabled === true && (cfg?.providers?.length ?? 0) > 0
+  } catch (err: unknown) {
+    console.warn('Failed to load web search global state:', err)
+    webSearchGlobalEnabled.value = false
+  }
+}
+
 // ── Platform Section type ──
 interface PlatformSection {
   platform: GroupPlatform
@@ -454,6 +485,7 @@ interface PlatformSection {
   group_ids: number[]
   model_mapping: Record<string, string>
   model_pricing: PricingFormEntry[]
+  web_search_emulation: boolean
 }
 
 // ── Table columns ──
@@ -565,7 +597,8 @@ function addPlatformSection(platform: GroupPlatform) {
     collapsed: false,
     group_ids: [],
     model_mapping: {},
-    model_pricing: []
+    model_pricing: [],
+    web_search_emulation: false,
   })
 }
 
@@ -679,10 +712,14 @@ function renameMappingKey(sectionIdx: number, oldKey: string, newKey: string) {
 }
 
 // ── Form ↔ API conversion ──
-function formToAPI(): { group_ids: number[], model_pricing: ChannelModelPricing[], model_mapping: Record<string, Record<string, string>> } {
+function formToAPI(): { group_ids: number[], model_pricing: ChannelModelPricing[], model_mapping: Record<string, Record<string, string>>, features_config: Record<string, unknown> } {
   const group_ids: number[] = []
   const model_pricing: ChannelModelPricing[] = []
   const model_mapping: Record<string, Record<string, string>> = {}
+  // Preserve existing features_config fields not managed by the form
+  const featuresConfig: Record<string, unknown> = editingChannel.value?.features_config
+    ? { ...editingChannel.value.features_config }
+    : {}
 
   for (const section of form.platforms) {
     if (!section.enabled) continue
@@ -711,7 +748,19 @@ function formToAPI(): { group_ids: number[], model_pricing: ChannelModelPricing[
     }
   }
 
-  return { group_ids, model_pricing, model_mapping }
+  // Collect web_search_emulation (only anthropic platform supports it)
+  const wsEmulation: Record<string, boolean> = {}
+  for (const section of form.platforms) {
+    if (!section.enabled) continue
+    if (section.web_search_emulation && section.platform === 'anthropic') {
+      wsEmulation[section.platform] = true
+    }
+  }
+  if (Object.keys(wsEmulation).length > 0) {
+    featuresConfig.web_search_emulation = wsEmulation
+  }
+
+  return { group_ids, model_pricing, model_mapping, features_config: featuresConfig }
 }
 
 function apiToForm(channel: Channel): PlatformSection[] {
@@ -755,13 +804,19 @@ function apiToForm(channel: Channel): PlatformSection[] {
         intervals: apiIntervalsToForm(p.intervals || [])
       } as PricingFormEntry))
 
+    // Read web_search_emulation from features_config
+    const fc = channel.features_config
+    const wsEmulation = fc?.web_search_emulation as Record<string, boolean> | undefined
+    const webSearchEnabled = wsEmulation?.[platform] === true
+
     sections.push({
       platform,
       enabled: true,
       collapsed: false,
       group_ids: groupIds,
       model_mapping: { ...mapping },
-      model_pricing: pricing
+      model_pricing: pricing,
+      web_search_emulation: webSearchEnabled,
     })
   }
 
@@ -786,10 +841,10 @@ async function loadChannels() {
     if (ctrl.signal.aborted || abortController !== ctrl) return
     channels.value = response.items || []
     pagination.total = response.total
-  } catch (error: any) {
-    if (error?.name === 'AbortError' || error?.code === 'ERR_CANCELED') return
-    appStore.showError(t('admin.channels.loadError', 'Failed to load channels'))
-    console.error('Error loading channels:', error)
+  } catch (error: unknown) {
+    const e = error as { name?: string; code?: string }
+    if (e?.name === 'AbortError' || e?.code === 'ERR_CANCELED') return
+    appStore.showError(extractApiErrorMessage(error, t('admin.channels.loadError', 'Failed to load channels')))
   } finally {
     if (abortController === ctrl) {
       loading.value = false
@@ -969,8 +1024,7 @@ async function handleSubmit() {
     }
   }
 
-  const { group_ids, model_pricing, model_mapping } = formToAPI()
-  console.log('[handleSubmit] model_pricing to send:', JSON.stringify(model_pricing))
+  const { group_ids, model_pricing, model_mapping, features_config } = formToAPI()
 
   submitting.value = true
   try {
@@ -983,7 +1037,8 @@ async function handleSubmit() {
         model_pricing,
         model_mapping: Object.keys(model_mapping).length > 0 ? model_mapping : {},
         billing_model_source: form.billing_model_source,
-        restrict_models: form.restrict_models
+        restrict_models: form.restrict_models,
+        features_config,
       }
       await adminAPI.channels.update(editingChannel.value.id, req)
       appStore.showSuccess(t('admin.channels.updateSuccess', 'Channel updated'))
@@ -995,19 +1050,18 @@ async function handleSubmit() {
         model_pricing,
         model_mapping: Object.keys(model_mapping).length > 0 ? model_mapping : {},
         billing_model_source: form.billing_model_source,
-        restrict_models: form.restrict_models
+        restrict_models: form.restrict_models,
+        features_config,
       }
       await adminAPI.channels.create(req)
       appStore.showSuccess(t('admin.channels.createSuccess', 'Channel created'))
     }
     closeDialog()
     loadChannels()
-  } catch (error: any) {
-    const msg = error.response?.data?.detail || (editingChannel.value
+  } catch (error: unknown) {
+    appStore.showError(extractApiErrorMessage(error, editingChannel.value
       ? t('admin.channels.updateError', 'Failed to update channel')
-      : t('admin.channels.createError', 'Failed to create channel'))
-    appStore.showError(msg)
-    console.error('Error saving channel:', error)
+      : t('admin.channels.createError', 'Failed to create channel')))
   } finally {
     submitting.value = false
   }
@@ -1045,9 +1099,8 @@ async function confirmDelete() {
     showDeleteDialog.value = false
     deletingChannel.value = null
     loadChannels()
-  } catch (error: any) {
-    appStore.showError(error.response?.data?.detail || t('admin.channels.deleteError', 'Failed to delete channel'))
-    console.error('Error deleting channel:', error)
+  } catch (error: unknown) {
+    appStore.showError(extractApiErrorMessage(error, t('admin.channels.deleteError', 'Failed to delete channel')))
   }
 }
 
@@ -1055,6 +1108,7 @@ async function confirmDelete() {
 onMounted(() => {
   loadChannels()
   loadGroups()
+  loadWebSearchGlobalState()
 })
 
 onUnmounted(() => {