feat(groups): add Claude Code client restriction and session isolation

- Add claude_code_only field to restrict groups to Claude Code clients only
- Add fallback_group_id for non-Claude Code requests to use alternate group
- Implement ClaudeCodeValidator for User-Agent detection
- Add group-level session binding isolation (groupID in Redis key)
- Prevent cross-group sticky session pollution
- Update frontend with Claude Code restriction controls

frontend/src/i18n/locales/en.ts

@@ -857,6 +857,15 @@ export default {
       imagePricing: {
         title: 'Image Generation Pricing',
         description: 'Configure pricing for gemini-3-pro-image model. Leave empty to use default prices.'
+      },
+      claudeCode: {
+        title: 'Claude Code Client Restriction',
+        tooltip: 'When enabled, this group only allows official Claude Code clients. Non-Claude Code requests will be rejected or fallback to the specified group.',
+        enabled: 'Claude Code Only',
+        disabled: 'Allow All Clients',
+        fallbackGroup: 'Fallback Group',
+        fallbackHint: 'Non-Claude Code requests will use this group. Leave empty to reject directly.',
+        noFallback: 'No Fallback (Reject)'
       }
     },
 

frontend/src/i18n/locales/zh.ts

@@ -934,6 +934,15 @@ export default {
       imagePricing: {
         title: '图片生成计费',
         description: '配置 gemini-3-pro-image 模型的图片生成价格，留空则使用默认价格'
+      },
+      claudeCode: {
+        title: 'Claude Code 客户端限制',
+        tooltip: '启用后，此分组仅允许 Claude Code 官方客户端访问。非 Claude Code 请求将被拒绝或降级到指定分组。',
+        enabled: '仅限 Claude Code',
+        disabled: '允许所有客户端',
+        fallbackGroup: '降级分组',
+        fallbackHint: '非 Claude Code 请求将使用此分组，留空则直接拒绝',
+        noFallback: '不降级（直接拒绝）'
       }
     },