feat: Complete HTML-first architecture implementation with API integration

- Replace value field with html_content for direct HTML storage
- Add original_template field for style detection preservation
- Remove all markdown processing from injector (delete markdown.go)
- Fix critical content extraction/injection bugs in engine
- Add missing UpdateContent PUT handler for content persistence
- Fix API client field names and add updateContent() method
- Resolve content type validation (only allow text/link types)
- Add UUID-based ID generation to prevent collisions
- Complete first-pass processing workflow for unprocessed elements
- Verify end-to-end: Enhancement → Database → API → Editor → Persistence

All 37 files updated for HTML-first content management system.
Phase 3a implementation complete and production ready.

internal/db/sqlite/querier.go

@@ -1,6 +1,6 @@
 // Code generated by sqlc. DO NOT EDIT.
 // versions:
-//   sqlc v1.29.0
+//   sqlc v1.30.0
 
 package sqlite
 
@@ -11,6 +11,7 @@ import (
 type Querier interface {
 	CreateContent(ctx context.Context, arg CreateContentParams) (Content, error)
 	CreateContentVersion(ctx context.Context, arg CreateContentVersionParams) error
+	DeleteAllSiteContent(ctx context.Context, siteID string) error
 	DeleteContent(ctx context.Context, arg DeleteContentParams) error
 	DeleteOldVersions(ctx context.Context, arg DeleteOldVersionsParams) error
 	GetAllContent(ctx context.Context, siteID string) ([]Content, error)