feat: complete HTML-first architecture implementation (Phase 1 & 2)

Major architectural simplification removing content type complexity:

Database Schema:
- Remove 'type' field from content and content_versions tables
- Simplify to pure HTML storage with html_content + original_template
- Regenerate all sqlc models for SQLite and PostgreSQL

API Simplification:
- Remove content type routing and validation
- Eliminate type-specific handlers (text/markdown/structured)
- Unified HTML-first approach for all content operations
- Simplify CreateContent and UpdateContent to HTML-only

Backend Enhancements:
- Update enhancer to only generate data-content-id (no data-content-type)
- Improve container expansion utilities with comprehensive block/inline rules
- Add Phase 3 preparation with boundary-respecting traversal logic
- Strengthen element classification for viable children detection

Documentation:
- Update TODO.md to reflect Phase 1-3 completion status
- Add WORKING_ON.md documenting the architectural transformation
- Mark container expansion and HTML-first architecture as complete

This completes the transition to a unified HTML-first content management system
with automatic style detection and element-based behavior, eliminating the
complex multi-type system in favor of semantic HTML-driven editing.

internal/db/queries/content.sql

@@ -1,38 +1,37 @@
 -- name: GetContent :one
-SELECT id, site_id, html_content, original_template, type, created_at, updated_at, last_edited_by
+SELECT id, site_id, html_content, original_template, created_at, updated_at, last_edited_by
 FROM content 
 WHERE id = sqlc.arg(id) AND site_id = sqlc.arg(site_id);
 
 -- name: GetAllContent :many
-SELECT id, site_id, html_content, original_template, type, created_at, updated_at, last_edited_by
+SELECT id, site_id, html_content, original_template, created_at, updated_at, last_edited_by
 FROM content 
 WHERE site_id = sqlc.arg(site_id)
 ORDER BY updated_at DESC;
 
 -- name: GetBulkContent :many
-SELECT id, site_id, html_content, original_template, type, created_at, updated_at, last_edited_by
+SELECT id, site_id, html_content, original_template, created_at, updated_at, last_edited_by
 FROM content 
 WHERE site_id = sqlc.arg(site_id) AND id IN (sqlc.slice('ids'));
 
 -- name: CreateContent :one
-INSERT INTO content (id, site_id, html_content, original_template, type, last_edited_by)
-VALUES (sqlc.arg(id), sqlc.arg(site_id), sqlc.arg(html_content), sqlc.arg(original_template), sqlc.arg(type), sqlc.arg(last_edited_by))
-RETURNING id, site_id, html_content, original_template, type, created_at, updated_at, last_edited_by;
+INSERT INTO content (id, site_id, html_content, original_template, last_edited_by)
+VALUES (sqlc.arg(id), sqlc.arg(site_id), sqlc.arg(html_content), sqlc.arg(original_template), sqlc.arg(last_edited_by))
+RETURNING id, site_id, html_content, original_template, created_at, updated_at, last_edited_by;
 
 -- name: UpdateContent :one
 UPDATE content 
-SET html_content = sqlc.arg(html_content), type = sqlc.arg(type), last_edited_by = sqlc.arg(last_edited_by)
+SET html_content = sqlc.arg(html_content), last_edited_by = sqlc.arg(last_edited_by)
 WHERE id = sqlc.arg(id) AND site_id = sqlc.arg(site_id)
-RETURNING id, site_id, html_content, original_template, type, created_at, updated_at, last_edited_by;
+RETURNING id, site_id, html_content, original_template, created_at, updated_at, last_edited_by;
 
 -- name: UpsertContent :one
-INSERT INTO content (id, site_id, html_content, original_template, type, last_edited_by)
-VALUES (sqlc.arg(id), sqlc.arg(site_id), sqlc.arg(html_content), sqlc.arg(original_template), sqlc.arg(type), sqlc.arg(last_edited_by))
+INSERT INTO content (id, site_id, html_content, original_template, last_edited_by)
+VALUES (sqlc.arg(id), sqlc.arg(site_id), sqlc.arg(html_content), sqlc.arg(original_template), sqlc.arg(last_edited_by))
 ON CONFLICT(id, site_id) DO UPDATE SET
     html_content = EXCLUDED.html_content,
-    type = EXCLUDED.type,
     last_edited_by = EXCLUDED.last_edited_by
-RETURNING id, site_id, html_content, original_template, type, created_at, updated_at, last_edited_by;
+RETURNING id, site_id, html_content, original_template, created_at, updated_at, last_edited_by;
 
 -- name: DeleteContent :exec
 DELETE FROM content 

internal/db/queries/versions.sql

@@ -1,22 +1,22 @@
 -- name: CreateContentVersion :exec
-INSERT INTO content_versions (content_id, site_id, html_content, original_template, type, created_by)
-VALUES (sqlc.arg(content_id), sqlc.arg(site_id), sqlc.arg(html_content), sqlc.arg(original_template), sqlc.arg(type), sqlc.arg(created_by));
+INSERT INTO content_versions (content_id, site_id, html_content, original_template, created_by)
+VALUES (sqlc.arg(content_id), sqlc.arg(site_id), sqlc.arg(html_content), sqlc.arg(original_template), sqlc.arg(created_by));
 
 -- name: GetContentVersionHistory :many
-SELECT version_id, content_id, site_id, html_content, original_template, type, created_at, created_by
+SELECT version_id, content_id, site_id, html_content, original_template, created_at, created_by
 FROM content_versions
 WHERE content_id = sqlc.arg(content_id) AND site_id = sqlc.arg(site_id)
 ORDER BY created_at DESC
 LIMIT sqlc.arg(limit_count);
 
 -- name: GetContentVersion :one
-SELECT version_id, content_id, site_id, html_content, original_template, type, created_at, created_by
+SELECT version_id, content_id, site_id, html_content, original_template, created_at, created_by
 FROM content_versions
 WHERE version_id = sqlc.arg(version_id);
 
 -- name: GetAllVersionsForSite :many
 SELECT 
-    cv.version_id, cv.content_id, cv.site_id, cv.html_content, cv.original_template, cv.type, cv.created_at, cv.created_by,
+    cv.version_id, cv.content_id, cv.site_id, cv.html_content, cv.original_template, cv.created_at, cv.created_by,
     c.html_content as current_html_content
 FROM content_versions cv
 LEFT JOIN content c ON cv.content_id = c.id AND cv.site_id = c.site_id