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.

server/internal/tenant/app/cache_support.go

@@ -88,6 +88,10 @@ func brandLibrarySummaryCacheKey(tenantID int64) string {
 	return fmt.Sprintf("brand:library_summary:%d", tenantID)
 }
 
+func tenantQuestionQuotaLockKey(tenantID int64) string {
+	return fmt.Sprintf("tenant:%d:question_quota", tenantID)
+}
+
 func brandDetailCacheKey(tenantID, brandID int64) string {
 	return fmt.Sprintf("brand:detail:%d:%d", tenantID, brandID)
 }