feat: add user preferences, agent name desensitization and related improvements

- Add user preferences persistence (model, migration, router, frontend core)
- Add agent name desensitization config
- Add agent_id to user custom prompts with migration
- Enhance agents persistence (base, memory, model, sql) and scheduler service
- Improve frontend agent cards/gallery, scheduled tasks, custom prompt menu
- Add pagination UI component; remove stale package-lock.json

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

offline-backend-20260512/backend/app/gateway/app.py

@@ -57,6 +57,7 @@ from app.gateway.routers import (
     thread_shares,
     threads,
     uploads,
+    user_preferences,
     user_prompts,
     writing,
 )
@@ -857,6 +858,9 @@ This gateway provides custom endpoints for models, MCP configuration, skills, an
 
     app.include_router(user_prompts.router)
 
+    # Per-user UI preferences at /api/user-preferences
+    app.include_router(user_preferences.router)
+
     # Roundtable-planning drafts + recommendation history at /api/roundtable-drafts
     app.include_router(roundtable_drafts.router)