Add backend API, running status and 30-day run history

- FastAPI + SQLite backend: tenants, jobs and runs, with an idempotent
  /api/v1/ingest endpoint authenticated by per-collector API keys
- Runs store started_at and finished_at; "Last Run" is the most recent
  finish, and in-progress runs show as Running
- Job modal shows a 30-day daily strip, success rate, and a filterable
  run list with per-run messages
- nginx: HTTPS plus basic auth, ingest endpoint exempt; systemd unit
- manage.py for API keys, job cleanup and demo data; pytest suite

Co-Authored-By: Claude Opus 5.5 <[email protected]>

backend/app/settings.py

@@ -0,0 +1,22 @@
+import os
+from dataclasses import dataclass
+from pathlib import Path
+
+# The modal shows this many days of run history; retention can never be shorter.
+HISTORY_DAYS = 30
+
+
+@dataclass(frozen=True)
+class Settings:
+    db_path: Path
+    retention_days: int = 90
+    # Dev only: serve ../public from the API so you can run without nginx.
+    serve_static: bool = False
+
+
+def load_settings() -> Settings:
+    return Settings(
+        db_path=Path(os.environ.get("BACKUP_DASH_DB", "backup-dashboard.db")),
+        retention_days=max(HISTORY_DAYS, int(os.environ.get("BACKUP_DASH_RETENTION_DAYS", "90"))),
+        serve_static=os.environ.get("BACKUP_DASH_SERVE_STATIC") == "1",
+    )