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]>

deploy/backup-dashboard-api.service

@@ -0,0 +1,23 @@
+[Unit]
+Description=Backup Dashboard API
+After=network.target
+
+[Service]
+User=backupdash
+Group=backupdash
+WorkingDirectory=/opt/backup-dashboard/backend
+Environment=BACKUP_DASH_DB=/var/lib/backup-dashboard/backup-dashboard.db
+Environment=BACKUP_DASH_RETENTION_DAYS=90
+# Bound to localhost: only nginx can reach it, so nginx's auth can't be bypassed from outside.
+# One worker is plenty at this scale and keeps SQLite writes simple.
+ExecStart=/opt/backup-dashboard/venv/bin/uvicorn --factory app.main:create_app --host 127.0.0.1 --port 8000 --proxy-headers
+Restart=on-failure
+
+StateDirectory=backup-dashboard
+NoNewPrivileges=true
+ProtectSystem=strict
+ProtectHome=true
+PrivateTmp=true
+
+[Install]
+WantedBy=multi-user.target