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/models/backup_schedule.py

@@ -0,0 +1,80 @@
+from __future__ import annotations
+
+from datetime import datetime, timezone
+from typing import Optional
+
+from sqlmodel import Field, SQLModel
+
+
+def _now() -> datetime:
+    return datetime.now(timezone.utc)
+
+
+FREQUENCIES = ["hourly", "daily", "weekly"]
+
+
+class BackupSchedule(SQLModel, table=True):
+    """An automatic, recurring backup of a local stack to a destination."""
+
+    id: Optional[int] = Field(default=None, primary_key=True)
+    stack_id: str
+    destination_id: int
+    frequency: str = "daily"  # one of FREQUENCIES
+    hour: int = 3  # UTC, used for daily/weekly
+    minute: int = 0
+    weekday: int = 0  # 0=Mon .. 6=Sun, used for weekly
+    include_volumes: bool = True
+    stop_first: bool = True
+    keep: int = 7  # retention: keep newest N for this stack on the dest (0 = all)
+    enabled: bool = True
+    last_run: Optional[datetime] = None
+    last_status: Optional[str] = None  # "ok" | "error: ..."
+    next_run: Optional[datetime] = None
+    created_at: datetime = Field(default_factory=_now)
+
+
+# --- API schemas ---
+
+
+class ScheduleCreate(SQLModel):
+    stack_id: str
+    destination_id: int
+    frequency: str = "daily"
+    hour: int = 3
+    minute: int = 0
+    weekday: int = 0
+    include_volumes: bool = True
+    stop_first: bool = True
+    keep: int = 7
+    enabled: bool = True
+
+
+class ScheduleUpdate(SQLModel):
+    destination_id: Optional[int] = None
+    frequency: Optional[str] = None
+    hour: Optional[int] = None
+    minute: Optional[int] = None
+    weekday: Optional[int] = None
+    include_volumes: Optional[bool] = None
+    stop_first: Optional[bool] = None
+    keep: Optional[int] = None
+    enabled: Optional[bool] = None
+
+
+class ScheduleRead(SQLModel):
+    id: int
+    stack_id: str
+    destination_id: int
+    destination_name: Optional[str]
+    frequency: str
+    hour: int
+    minute: int
+    weekday: int
+    include_volumes: bool
+    stop_first: bool
+    keep: int
+    enabled: bool
+    last_run: Optional[datetime]
+    last_status: Optional[str]
+    next_run: Optional[datetime]
+    created_at: datetime