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.

cmd/serve.go

@@ -221,6 +221,7 @@ func runServe(cmd *cobra.Command, args []string) {
 			contentRouter.Get("/{id}", contentHandler.GetContent)
 			contentRouter.Get("/", contentHandler.GetAllContent)
 			contentRouter.Post("/", contentHandler.CreateContent)
+			contentRouter.Put("/{id}", contentHandler.UpdateContent)
 
 			// Version control endpoints
 			contentRouter.Get("/{id}/versions", contentHandler.GetContentVersions)