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

backend/migrations/029_add_group_claude_code_restriction.sql

@@ -0,0 +1,21 @@
+-- 029_add_group_claude_code_restriction.sql
+-- 添加分组级别的 Claude Code 客户端限制功能
+
+-- 添加 claude_code_only 字段：是否仅允许 Claude Code 客户端
+ALTER TABLE groups
+ADD COLUMN IF NOT EXISTS claude_code_only BOOLEAN NOT NULL DEFAULT FALSE;
+
+-- 添加 fallback_group_id 字段：非 Claude Code 请求降级到的分组
+ALTER TABLE groups
+ADD COLUMN IF NOT EXISTS fallback_group_id BIGINT REFERENCES groups(id) ON DELETE SET NULL;
+
+-- 添加索引优化查询
+CREATE INDEX IF NOT EXISTS idx_groups_claude_code_only
+ON groups(claude_code_only) WHERE deleted_at IS NULL;
+
+CREATE INDEX IF NOT EXISTS idx_groups_fallback_group_id
+ON groups(fallback_group_id) WHERE deleted_at IS NULL AND fallback_group_id IS NOT NULL;
+
+-- 添加字段注释
+COMMENT ON COLUMN groups.claude_code_only IS '是否仅允许 Claude Code 客户端访问此分组';
+COMMENT ON COLUMN groups.fallback_group_id IS '非 Claude Code 请求降级使用的分组 ID';