feat: add Skill API endpoints

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/main.py

@@ -13,6 +13,7 @@ from app.routers import (
     todo_router,
     settings_router,
     folder_router,
+    skill_router,
 )
 from app.routers.scheduler import router as scheduler_router
 from app.services.scheduler_service import start_scheduler, stop_scheduler, get_scheduler_status
@@ -59,6 +60,7 @@ app.include_router(agent_router)
 app.include_router(todo_router)
 app.include_router(settings_router)
 app.include_router(folder_router)
+app.include_router(skill_router)
 app.include_router(scheduler_router)