fix(docker): keep server Postgres on ./data/postgres, move Windows volume to an override

751cac7 switched the base compose file to an external named volume
(bellsystems-postgres-data) to dodge a WSL2/Docker Desktop bind-mount bug.
That volume only exists on the Windows dev machine: on the VPS, where the
push auto-deploys via deploy-host.sh, `docker compose up` would fail on the
missing external volume (or, if created, start Postgres on an empty
database while the real data sat unused in ./data/postgres).

The base file goes back to the ./data/postgres bind mount the server has
always used (Linux has no such bug). The named volume now lives in
docker-compose.override.yml, which Compose loads automatically, is
gitignored, and is created from docker-compose.override.example.yml on
Windows machines only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docker-compose.yml

@@ -50,7 +50,10 @@ services:
       POSTGRES_USER: ${POSTGRES_USER}
       POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
     volumes:
-      - postgres-data:/var/lib/postgresql/data
+      # Server default: plain folder on the host (Linux, no WSL2 issues).
+      # Windows dev machines override this with a Docker volume in
+      # docker-compose.override.yml — see docker-compose.override.example.yml.
+      - ./data/postgres:/var/lib/postgresql/data
     networks:
       - internal
     healthcheck:
@@ -62,17 +65,3 @@ services:
 networks:
   internal:
     driver: bridge
-
-volumes:
-  # Docker-managed volume (lives inside the WSL2 VM's own filesystem) instead
-  # of a ./data/postgres bind mount onto the Windows filesystem. The bind
-  # mount hit a WSL2/Docker Desktop bug where the 9p/virtiofs bridge reports
-  # normal postgres:postgres 0600 ownership but the kernel still refuses the
-  # postgres user's own open() calls for write — silent on read, fatal on any
-  # WAL write, which took the whole database down after an unclean shutdown.
-  # Migrated 2026-09-04; the old bind-mounted data is untouched at
-  # ./data/postgres/ as a backup (that folder itself was too wedged by the
-  # same bug to even rename — leave it alone; it's not used anymore).
-  postgres-data:
-    name: bellsystems-postgres-data
-    external: true