Phase 7: scheduled (recurring) backups (0.7.0)

- BackupSchedule model + schedule_service: next-run calc (hourly/daily/weekly,
  UTC), background scheduler loop (lifespan), run-one with retention pruning
  (keep newest N per stack on the destination), backup_failed notify event.
- routers/schedules.py: schedules CRUD + run-now; registered in main.py.
- Frontend: api/schedules.ts + Settings → Scheduled backups (list with next/last
  run + status, enable/disable, run-now, delete; add form with stack/destination/
  frequency/time/weekday/retention/volumes).

Rough-verified only (per request): py_compile, frontend tsc build, app import
(95 routes), next-run math sanity. Full live run to be tested after deploy.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/main.py

@@ -22,6 +22,7 @@ from routers import (
     editor,
     images,
     ports,
+    schedules,
     settings as settings_router,
     stacks,
     system,
@@ -29,7 +30,7 @@ from routers import (
     volumes,
     ws,
 )
-from services import update_service
+from services import schedule_service, update_service
 
 logging.basicConfig(level=logging.INFO)
 logger = logging.getLogger("stackpilot")
@@ -45,12 +46,14 @@ async def lifespan(app: FastAPI):
     except Exception as exc:  # noqa: BLE001
         logger.warning("Stack discovery failed: %s", exc)
     update_task = asyncio.create_task(update_service.background_loop())
+    schedule_task = asyncio.create_task(schedule_service.scheduler_loop())
     logger.info("StackPilot backend ready on port %s", settings.PORT)
     yield
     update_task.cancel()
+    schedule_task.cancel()
 
 
-app = FastAPI(title="StackPilot", version="0.6.0", lifespan=lifespan)
+app = FastAPI(title="StackPilot", version="0.7.0", lifespan=lifespan)
 
 app.add_middleware(
     CORSMiddleware,
@@ -81,6 +84,7 @@ app.include_router(audit.router)
 app.include_router(settings_router.router)
 app.include_router(backups.router)
 app.include_router(destinations.router)
+app.include_router(schedules.router)
 app.include_router(agents.router)
 app.include_router(ws.router)