fix(compose): drop vestigial uploads mount from db service

The db service mounted ./uploads:/app/uploads, which Postgres has never
used and nothing in the repo relies on: no SQL COPY TO/pg_dump path, no
doc/test reference to an uploads path inside the db container (the only
/app/uploads mentions in TEST_DATA.md are the app/test containers), and
the backup scan is app-side.

Forensics: the mount was introduced by accident in 6ebe9749 ("Simplify
docker-compose healthcheck configuration"), which incidentally REPLACED
the db service's volumes with the app service's uploads mount. The
follow-up 91456d11 ("restore essential database configuration")
restored postgres_data and the schema-init mount but nobody noticed the
stray uploads mount riding along, and it has survived every compose
refactor since.

The tests service in docker-compose.dev.yml keeps its own ./uploads
mount — that is the app-like test runner (TEST_UPLOAD_PATH=/app/uploads)
and is legitimate. The dev db inherits its volumes from the base file,
so it is fixed automatically.

docker-compose.yml

@@ -12,8 +12,6 @@ services:
     volumes:
       - postgres_data:/var/lib/postgresql/data
       - ./database/schema:/docker-entrypoint-initdb.d
-      # Make other volumes as needed
-      - ./uploads:/app/uploads
     ports:
       - "127.0.0.1:${DB_PORT:-5432}:${DB_PORT:-5432}"
       - "[::1]:${DB_PORT:-5432}:${DB_PORT:-5432}"