Document Postgres on citadel, drop stale omarchy references

The database moved to citadel (192.168.50.195); .env and the deployed
container already point there, but env.example still handed out the old
omarchy address.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EWRh3vxBcqwDbuWv2dfQYF

CLAUDE.md

@@ -37,7 +37,7 @@ Docker runs alongside local dev on different ports and databases:
 - **Framework:** Kit (Integrant-based)
 - **Server:** Undertow
 - **Routing:** Reitit
-- **Database:** PostgreSQL + conman + Migratus
+- **Database:** PostgreSQL + conman + Migratus — the Postgres lives on **citadel** (`192.168.50.195:5432`); `btcprice` for local dev, `btcprod` for the deployed container
 - **Port:** 4100 (env: BTCDATA_PORT)
 - **CORS:** Configured via CORS_ORIGIN env var