feat(channel-monitor): request templates with snapshot apply + headers/body override

Problem:
Upstream channels can reject monitor probes based on client fingerprint
(e.g. "only Claude Code clients allowed"). The monitor had no way to
customize the outgoing request to bypass such restrictions.

Solution:
Introduce reusable request templates that carry extra_headers plus an
optional body override; monitors reference a template and receive a
snapshot copy on apply. Template edits do NOT auto-propagate — users
must click "apply to associated monitors" to refresh snapshots, so a
bad template edit cannot instantly break all production monitors.

Data model (migration 112):
- channel_monitor_request_templates: id, name, provider, description,
  extra_headers jsonb, body_override_mode ('off'|'merge'|'replace'),
  body_override jsonb. Unique (provider, name).
- channel_monitors: +template_id (FK, ON DELETE SET NULL), +extra_headers,
  +body_override_mode, +body_override (the three runtime snapshot fields).

Checker (channel_monitor_checker.go):
- callProvider + runCheckForModel accept a CheckOptions carrying the
  snapshot fields. mergeHeaders applies user headers on top of adapter
  defaults (forbidden list: Host / Content-Length / Transfer-Encoding /
  Connection / Content-Encoding).
- buildRequestBody:
    off     -> adapter default body
    merge   -> shallow-merge over default; per-provider deny list
               (model/messages/contents) protects the challenge contract
    replace -> user body verbatim
- Replace mode skips challenge validation; instead HTTP 2xx + non-empty
  extracted response text = operational, empty = failed.
- 4 new unit tests cover all three modes + replace/empty-response case.

Admin API:
- /admin/channel-monitor-templates CRUD + /:id/apply (overwrite snapshot
  on all template_id=id monitors, returns affected count).
- channel_monitor request/response DTOs gain the 4 new fields.

Frontend:
- channelMonitorTemplate.ts API client.
- MonitorAdvancedRequestConfig.vue shared component for headers textarea
  + body mode radio + body JSON editor; used by both template and monitor
  forms.
- MonitorTemplateManagerDialog.vue: provider tabs, list/create/edit/
  delete/apply, live "associated monitors" count per row.
- MonitorFiltersBar: new 模板管理 button next to 新增监控.
- MonitorFormDialog: collapsible 高级 section with template dropdown
  (filtered by form.provider, clears on provider change) + embedded
  AdvancedRequestConfig. Picking a template copies its fields into the
  form (snapshot semantics mirrored on the client).
- i18n zh/en entries for all new copy.

chore: bump version to 0.1.114.32

frontend/src/i18n/locales/zh.ts

@@ -2235,7 +2235,57 @@ export default {
       },
       runResultTitle: '检测结果',
       noMonitorsYet: '暂无监控',
-      createFirstMonitor: '创建第一个监控来跟踪渠道可用性'
+      createFirstMonitor: '创建第一个监控来跟踪渠道可用性',
+      advanced: {
+        section: '高级（可选）',
+        sectionHint: '自定义请求头和请求体，用于突破上游的客户端识别限制（如仅允许 Claude Code 客户端）。',
+        headers: '自定义请求头',
+        headersPlaceholder: 'User-Agent: claude-cli/1.0.83 (external, cli)\nx-app: cli\nanthropic-beta: claude-code-20250219',
+        headersHint: '每行一对 Key: Value；会与默认请求头合并，用户值优先。hop-by-hop 类 header（Host/Content-Length/...）会被忽略。',
+        headersParseError: '无法解析这一行：{line}',
+        bodyMode: '请求体处理',
+        bodyModeOff: '默认',
+        bodyModeMerge: '合并',
+        bodyModeReplace: '覆盖',
+        bodyModeHintOff: '使用 adapter 默认请求体（带 challenge 数学题校验）。',
+        bodyModeHintMerge: '与默认请求体浅合并，用户字段优先；但 model / messages / contents 会被保护不允许覆盖（动这些字段请用「覆盖」模式）。',
+        bodyModeHintReplace: '完全用下方 JSON 作为请求体。注意：此模式下跳过 challenge 校验，改为 HTTP 2xx + 响应文本非空即视为可用。',
+        bodyJson: 'Body JSON',
+        bodyJsonHint: '失焦时自动解析校验。留空等价于没有覆盖。',
+        bodyJsonError: 'JSON 解析失败',
+        bodyJsonObjectError: '请求体必须是一个 JSON 对象（不能是数组或基本类型）'
+      },
+      templateField: {
+        label: '请求模板',
+        none: '不使用模板',
+        placeholder: '选择一个模板（按当前平台过滤）',
+        applyHint: '选中模板后，会把模板的请求头和请求体拷贝到此监控（快照）。后续模板变动不自动同步。'
+      },
+      template: {
+        manageButton: '模板管理',
+        managerTitle: '请求模板管理',
+        createButton: '新建模板',
+        emptyState: '当前平台下还没有请求模板',
+        missingName: '请输入模板名称',
+        createSuccess: '模板创建成功',
+        updateSuccess: '模板更新成功',
+        deleteSuccess: '模板删除成功',
+        applyButton: '应用到关联监控',
+        applyTooltip: '把当前模板配置覆盖到所有关联的监控上',
+        applyTitle: '应用模板',
+        applyConfirm: '确认应用',
+        applyConfirmMessage: '将把模板「{name}」的当前配置覆盖到 {n} 个关联监控。监控本地已编辑的自定义修改会被丢弃，是否继续？',
+        applySuccess: '已应用到 {n} 个监控',
+        deleteConfirm: '确定要删除模板「{name}」吗？{n} 个关联监控会解除关联但保留自己的快照继续工作。',
+        associatedCount: '{n} 个关联监控',
+        headersSummary: '{n} 个自定义请求头',
+        form: {
+          name: '模板名称',
+          namePlaceholder: '例：Claude Code 伪装',
+          description: '说明',
+          descriptionPlaceholder: '可选：说明这个模板的用途和来源（抓包日期等）'
+        }
+      }
     },
 
     // Subscriptions Management