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>

CLAUDE.md

@@ -42,7 +42,7 @@ Dereth Tracker is a real-time telemetry platform for Asheron's Call world tracki
 - Connection pool: `min_size=5, max_size=100, command_timeout=120` (`db_async.py:21`). Postgres `max_connections` is the default 100, shared with Grafana and the agent's read-only role — don't widen the pool further.
 - Persisted event types: telemetry, spawn, rare, portal, character_stats, combat_stats. Everything else (vitals, quest, cantrips, nearby_objects, dungeon_map, share_*) is memory-only.
 - Read-only agent role `overlord_agent_ro` is provisioned manually via `agent/sql/0001_overlord_agent_ro.sql` (SELECT-only).
-- There is **no backup mechanism** — durability is the two Docker volumes (`timescale-data`, `inventory-data`).
+- Backups: nightly cron on the host runs `scripts/backup-databases.sh` (pg_dump both DBs to `/home/erik/backups/postgres/`, 7-day retention; telemetry/spawn hypertable data deliberately excluded). Restore procedure: `docs/backups.md` — TimescaleDB needs `timescaledb_pre_restore()/post_restore()`.
 - `db.py` is a dead legacy SQLite layer — nothing imports it. All persistence goes through `db_async.py`.
 
 ## Route conventions