feat(dashboard): GET /api/dashboard endpoint

Task 2 of #583. Minimal login-gated blueprint returning build_dashboard(uid);
registered in the app factory.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/fabledassistant/app.py

@@ -27,6 +27,7 @@ from fabledassistant.routes.profile import profile_bp
 from fabledassistant.routes.knowledge import knowledge_bp
 from fabledassistant.routes.rulebooks import rulebooks_bp
 from fabledassistant.routes.trash import trash_bp
+from fabledassistant.routes.dashboard import dashboard_bp
 from fabledassistant.mcp import mount_mcp
 
 STATIC_DIR = Path(__file__).parent / "static"
@@ -87,6 +88,7 @@ def create_app() -> Quart:
     app.register_blueprint(knowledge_bp)
     app.register_blueprint(rulebooks_bp)
     app.register_blueprint(trash_bp)
+    app.register_blueprint(dashboard_bp)
 
     @app.before_request
     async def before_request():