feat(shared): add errors lib, question-content, and update permissions and UI

- Add errors lib for standardized error handling

- Add question-content lib for question content processing

- Update action-utils, ai/provider-config, auth-guard, permissions, types/permissions

- Update UI sheet component

- Update proxy middleware

src/shared/lib/action-utils.ts

@@ -8,7 +8,7 @@
  */
 
 import type { ActionState } from "@/shared/types/action-state"
-import { PermissionDeniedError } from "@/shared/lib/auth-guard"
+import { PermissionDeniedError } from "@/shared/lib/errors"
 
 /**
  * 已知的业务错误类型,消息可以安全返回给客户端。