fix(infra): mount Postgres 18+ canon (/var/lib/postgresql)

Postgres 18 mudou o layout do mount canônico — dados ficam em subdir por
major-version (18/main) pra suportar pg_upgrade --link sem boundary
issues. Ref: docker-library/postgres#1259.

Antes: container subia em loop com "in 18+, these Docker images are
configured to store database data in a format compatible with
pg_ctlcluster" e "there appears to be PostgreSQL data in:
/var/lib/postgresql/data (unused mount/volume)".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker-compose.dev.yml

@@ -16,7 +16,10 @@ services:
     ports:
       - '5432:5432'
     volumes:
-      - sar-postgres-data:/var/lib/postgresql/data
+      # Postgres 18+ usa /var/lib/postgresql (sem /data) — dados ficam em
+      # subdir por major-version pra suportar pg_upgrade --link sem
+      # boundary issues. Ref: docker-library/postgres#1259.
+      - sar-postgres-data:/var/lib/postgresql
       - ./scripts/postgres-init:/docker-entrypoint-initdb.d:ro
     healthcheck:
       test: ['CMD-SHELL', 'pg_isready -U sar -d sar_master']