Deploy: fix the initdb race that made migrate time out

On a real Synology first run, `migrate` exited 1 with a bare asyncpg
TimeoutError while the postgres log showed a perfectly healthy server.

The healthcheck was `pg_isready` with no -h, so it checked the UNIX SOCKET.
During first-time initialisation the postgres image runs a temporary server
that listens on the socket only (listen_addresses=''), so pg_isready answered
and the container was marked healthy while nothing was listening on TCP yet.
Dependents then connected to postgres:5432, hung, and timed out. It only bites
on the very first start of a fresh data directory, which is exactly the run an
operator is doing when they have least idea what is wrong.

- healthcheck uses `pg_isready -h 127.0.0.1 -p 5432`, so health means TCP is
  actually accepting.
- `migrate` additionally waits for the port itself (DB_WAIT_SECONDS, default
  180) before running alembic. It is a one-shot with no restart policy, so a
  few seconds of slow NAS disk should not fail the whole bring-up; the API and
  workers already self-heal through their restart policy.

Verified with a first-time bring-up against a fresh data directory: migrate
logs "database accepting connections", applies core + all four plugin
branches, and the stack comes up serving.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nux3LCu4zP9nih4BRhPyHw

docker/entrypoint.sh

@@ -24,7 +24,35 @@ set -eu
 cmd="${1:-api}"
 [ "$#" -gt 0 ] && shift || true
 
+# Belt and braces on top of the compose healthcheck: a NAS with slow disks can
+# take a while over initdb, and `migrate` is a one-shot with no restart policy —
+# if it starts a moment early it fails the whole bring-up.
+wait_for_db() {
+    python - <<'PYEOF'
+import os, socket, sys, time
+from urllib.parse import urlparse
+
+url = os.environ.get("DATABASE_URL", "")
+parsed = urlparse(url.replace("+asyncpg", ""))
+host = parsed.hostname or "postgres"
+port = parsed.port or 5432
+deadline = time.time() + float(os.environ.get("DB_WAIT_SECONDS", "180"))
+
+while time.time() < deadline:
+    try:
+        with socket.create_connection((host, port), timeout=3):
+            print(f"[entrypoint] database accepting connections at {host}:{port}")
+            sys.exit(0)
+    except OSError:
+        time.sleep(2)
+
+print(f"[entrypoint] ERROR: {host}:{port} never accepted a connection", file=sys.stderr)
+sys.exit(1)
+PYEOF
+}
+
 run_migrations() {
+    wait_for_db
     echo "[entrypoint] core schema: alembic upgrade head"
     alembic upgrade head
     for plugin in $ENABLED_PLUGINS; do