chore(docker): seeder service pre-creates unprefixed 'admin' user row

Alerting + outbound controllers resolve acting user via
authentication.name with 'user:' prefix stripped → 'admin'. But
UserRepository.upsert stores env-admin as 'user:admin' (JWT sub format).
The resulting FK mismatch manifests as 500 'alert_rules_created_by_fkey'
on any create operation in a fresh docker stack.

Workaround: run-once 'cameleer-seed' compose service runs psql against
deploy/docker/postgres-init.sql after the server is healthy (i.e. after
Flyway migrations have created tenant_default.users), inserting
user_id='admin' idempotently. The root-cause fix belongs in the backend
(either stop stripping the prefix in alerting/outbound controllers, or
normalise storage to the unprefixed form) and is out of scope for
Plan 03.

docker-compose.yml

@@ -130,6 +130,25 @@ services:
       retries: 10
     restart: unless-stopped
 
+  # Run-once seeder: waits for the server to be healthy (i.e. Flyway migrations
+  # finished) and inserts a `user_id='admin'` row (without the `user:` prefix)
+  # so alerting-controller FKs succeed. See deploy/docker/postgres-init.sql for
+  # the full rationale. Idempotent — exits 0 if the row already exists.
+  cameleer-seed:
+    image: postgres:16
+    container_name: cameleer-seed
+    depends_on:
+      cameleer-server:
+        condition: service_healthy
+    environment:
+      PGPASSWORD: cameleer_dev
+    volumes:
+      - ./deploy/docker/postgres-init.sql:/seed.sql:ro
+    entrypoint: ["sh", "-c"]
+    command:
+      - "psql -h cameleer-postgres -U cameleer -d cameleer -v ON_ERROR_STOP=1 -f /seed.sql"
+    restart: "no"
+
 volumes:
   cameleer-pgdata:
   cameleer-chdata: