fix(docker): auto-build schema on a fresh DB via docker-entrypoint-initdb.d

Root cause of 'data lost on every rebuild': nothing created the Postgres schema. TypeORM is synchronize:false, the API container runs no migration step, and there was no init mount — so a fresh pg_data volume came up with ZERO tables (empty/broken DB; the schema had only ever been loaded manually). Mount backend/migrations/*.sql into /docker-entrypoint-initdb.d so Postgres auto-applies the full schema (001..021, plain SQL) ON FIRST INIT ONLY. Existing volumes are untouched (initdb scripts run only on an empty data dir); a fresh volume now self-heals the schema. NOTE: actual row DATA still persists only while the pg_data named volume persists — 'docker compose down' keeps it across 'build --no-cache'; 'down -v' / volume prune is the only thing that wipes it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker/docker-compose.yml

@@ -8,6 +8,13 @@ services:
       POSTGRES_PASSWORD: ${DB_PASSWORD:-corrosion_dev}
     volumes:
       - pg_data:/var/lib/postgresql/data
+      # Auto-build the schema on a FRESH database. Postgres runs these ONLY when
+      # the data dir is empty (first boot or after a volume reset), so it never
+      # touches an existing volume — it just makes a fresh DB self-heal: the full
+      # schema is applied in order from the sqlx migrations (001..NNN), then the
+      # API's bootstrap seeds the admin. Rebuilds (with the volume kept) are a
+      # no-op here; the data persists. Only `down -v` / volume prune loses data.
+      - ../backend/migrations:/docker-entrypoint-initdb.d:ro
     ports:
       - "8101:5432"
     healthcheck: