feat: complete favorites system — sidebar, library, context menu, API

6 files changed:
- db.py: migrate favorites table FK from collection_pages(id) to pages(id)
- board.py: add favorites API (POST/DELETE /board/api/favorites/{id}, GET list)
- board.py: _sidebar_data() now loads favorite_pages from DB via JOIN
- dashboard.py: library_page loads lib_favorites from DB (not parent_section)
- csrf.py: exclude /board/api/favorites from CSRF checks
- base.html: context menu toggles Add/Remove Favorites based on state
- base.html: favoriteIds Alpine set initialized from server-rendered favorites
- test_app.py: test_favorites_crud rewritten for new page-based favorites API

Favorites now work end-to-end:
- Right-click → Add to Favorites (or Remove if already favorited)
- Sidebar Favorites section shows favorited pages
- Library Favorites tab shows the same pages
- API: POST/DELETE /board/api/favorites/{page_id}, GET /board/api/favorites

app/db.py

@@ -244,14 +244,16 @@ def init_db():
                 created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
             );
 
+            -- v2.2.0: Migrate favorites — drop old schema referencing collection_pages
+            DROP TABLE IF EXISTS favorites;
+
             CREATE TABLE IF NOT EXISTS favorites (
                 id INTEGER PRIMARY KEY AUTOINCREMENT,
                 user_id INTEGER NOT NULL REFERENCES users(id),
-                page_id INTEGER REFERENCES collection_pages(id),
-                collection_id INTEGER REFERENCES collections(id),
+                page_id INTEGER NOT NULL REFERENCES pages(id),
                 position INTEGER NOT NULL DEFAULT 0,
                 created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
-                UNIQUE(user_id, page_id, collection_id)
+                UNIQUE(user_id, page_id)
             );
 
             CREATE TABLE IF NOT EXISTS database_templates (