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/shared/config/reload.go

@@ -62,7 +62,7 @@ func Diff(previous, current *Config) []FieldChange {
 	if !reflect.DeepEqual(previous.Membership, current.Membership) {
 		addChange("membership", true)
 	}
-	if previous.BrandLibrary != current.BrandLibrary {
+	if !reflect.DeepEqual(previous.BrandLibrary, current.BrandLibrary) {
 		addChange("brand_library", true)
 	}
 	if previous.Qdrant != current.Qdrant {