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>

frontend/src/api/schedules.ts

@@ -0,0 +1,49 @@
+import api from "./client";
+
+export interface BackupSchedule {
+  id: number;
+  stack_id: string;
+  destination_id: number;
+  destination_name: string | null;
+  frequency: "hourly" | "daily" | "weekly";
+  hour: number;
+  minute: number;
+  weekday: number;
+  include_volumes: boolean;
+  stop_first: boolean;
+  keep: number;
+  enabled: boolean;
+  last_run: string | null;
+  last_status: string | null;
+  next_run: string | null;
+  created_at: string;
+}
+
+export interface ScheduleInput {
+  stack_id: string;
+  destination_id: number;
+  frequency: string;
+  hour: number;
+  minute: number;
+  weekday: number;
+  include_volumes: boolean;
+  stop_first: boolean;
+  keep: number;
+  enabled: boolean;
+}
+
+export const schedulesApi = {
+  list: () => api.get<BackupSchedule[]>("/api/backups/schedules").then((r) => r.data),
+  create: (body: ScheduleInput) =>
+    api.post<BackupSchedule>("/api/backups/schedules", body).then((r) => r.data),
+  update: (id: number, body: Partial<ScheduleInput>) =>
+    api.put<BackupSchedule>(`/api/backups/schedules/${id}`, body).then((r) => r.data),
+  remove: (id: number) =>
+    api.delete(`/api/backups/schedules/${id}`).then((r) => r.data),
+  run: (id: number) =>
+    api
+      .post<{ ok: boolean; name?: string; destination?: string; error?: string }>(
+        `/api/backups/schedules/${id}/run`
+      )
+      .then((r) => r.data),
+};