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/timeutil.py

@@ -0,0 +1,12 @@
+from datetime import UTC, datetime
+
+# Every timestamp in the DB uses this exact format, so string comparison == chronological comparison.
+DB_FORMAT = "%Y-%m-%dT%H:%M:%SZ"
+
+
+def utcnow() -> datetime:
+    return datetime.now(UTC).replace(microsecond=0)
+
+
+def to_db(dt: datetime) -> str:
+    return dt.astimezone(UTC).strftime(DB_FORMAT)