security: enforce real plugin secret, fix proxy auth bypass, loopback DB ports, nightly backups

- SHARED_SECRET now read from env and fail-closed: unset/placeholder refuses
  ALL plugin connections (constant-time compare). The old hardcoded
  'your_shared_secret' in this public repo was no auth at all. Dockerfile
  default removed; generate_data.py reads the env var.
- SECRET_KEY fails closed at startup (main.py and agent/auth.py) instead of
  falling back to a publicly-known signing key; agent systemd unit now
  requires /etc/overlord/agent.env (no '-' prefix).
- AuthMiddleware + /ws/live: replace the 172.x source-IP trust (which every
  nginx-proxied internet request satisfied via docker-proxy — full session
  bypass and unauthenticated in-game command injection) with
  private-source AND no X-Forwarded-For, i.e. only genuinely internal
  callers (overlord-agent on the host, compose-network services). Invariant
  documented in nginx/overlord.conf: every tracker-bound location must set
  X-Forwarded-For.
- /character-stats/test endpoints gated behind admin (they upsert real rows).
- docker-compose: bind 5432/5433 to 127.0.0.1 (both DBs were internet-
  reachable; active brute-force observed in dereth-db logs).
- discord-rare-monitor: drop dead SHARED_SECRET constant.
- scripts/backup-databases.sh + docs/backups.md: nightly pg_dump of both DBs
  (telemetry/spawn hypertable data excluded), 10MB canary, umask 077,
  TimescaleDB restore procedure.
- Remove stray mangled-path css file from repo root.

Adversarially reviewed pre-deploy (3-lens workflow): ship verdict; deploy-
sequencing blockers addressed (secret staged before enforcement, exec bit
set, cron uses bash).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

discord-rare-monitor/discord_rare_monitor.py

@@ -34,7 +34,6 @@ logger = logging.getLogger(__name__)
 # Configuration from environment variables
 DISCORD_TOKEN = os.getenv('DISCORD_RARE_BOT_TOKEN')
 WEBSOCKET_URL = os.getenv('DERETH_TRACKER_WS_URL', 'ws://dereth-tracker:8765/ws/live')
-SHARED_SECRET = 'your_shared_secret'
 ACLOG_CHANNEL_ID = int(os.getenv('ACLOG_CHANNEL_ID', '1349649482786275328'))
 COMMON_RARE_CHANNEL_ID = int(os.getenv('COMMON_RARE_CHANNEL_ID', '1355328792184226014'))
 GREAT_RARE_CHANNEL_ID = int(os.getenv('GREAT_RARE_CHANNEL_ID', '1353676584334131211'))