feat(admin-brand): add question expansion service and related functionality

- Implemented QuestionExpansionService for generating and materializing questions based on combinations and AI distillation.
- Added question metadata classification logic to infer intent and layer of questions.
- Created API handlers for question expansion operations including combination preview, AI distillation, metadata classification, and materialization.
- Introduced database migrations to support new question-related fields and constraints in brand_questions and brand_keywords tables.
- Added caching mechanism for AI distillation results to improve performance.
- Defined JSON schemas for question distillation responses to ensure data integrity.

apps/admin-web/src/lib/errors.ts

@@ -67,7 +67,13 @@ const errorMessageMap: Record<string, string> = {
   brand_limit_reached: '品牌公司数量已达当前套餐上限',
   keyword_exists: '关键词已存在',
   keyword_limit_reached: '关键词数量已达当前套餐上限',
-  question_limit_reached: '当前关键词下的问题数量已达上限',
+  question_exists: '该品牌下已存在相同问题',
+  no_valid_questions: '没有可保存的问题，请调整候选后重试',
+  invalid_enum: '请求枚举值不合法',
+  llm_timeout: 'AI 扩展超时，AI 点已退还',
+  llm_invalid_output: 'AI 输出无法解析，AI 点已退还',
+  materialize_failed: '保存问题失败，请稍后重试',
+  question_limit_reached: '当前账号问题数量已达上限',
   knowledge_text_name_too_long: '文本名称不能超过 20 个字',
   brand_not_found: '品牌不存在或已删除',
   keyword_not_found: '关键词不存在或已删除',