feat(544): shipped compose files run on the orchestrator's defaults; the app waits for its database itself

Brings the three compose files in line with rule 198 (milestone 544,
step 6203, at the operator's request):
- no healthcheck on the app or the database, so a slow pg_isready on
  stalled storage can no longer get a working database killed;
- no deploy.restart_policy in the Swarm file, so Swarm's default
  (condition: any) restarts clean exits too, instead of on-failure with
  max_attempts leaving the app down;
- depends_on is plain start order; restart: unless-stopped stays on the
  plain-Compose files (Swarm ignores it), and the dev app gains it.

The orchestrator used to be what retried a container that started before
Postgres was ready. That is now the app's job: alembic/env.py calls
services/db_ready.wait_for_database before migrating. It retries refused
connections, unresolved hosts, connect timeouts and "the database system
is starting up" with 1-2-4-...-10s spacing for up to 300s, then exits
non-zero; a wrong password or missing database fails at once.
Per-request recovery is the engine's pool_pre_ping.

Also fixes the dev compose database image: postgres:16-alpine has no
vector extension, so migrations could not run against it. It now uses
pgvector/pgvector:pg17 like the other two files.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

alembic/env.py

@@ -6,6 +6,7 @@ from sqlalchemy.ext.asyncio import create_async_engine
 
 from scribe.config import Config
 from scribe.models import Base
+from scribe.services.db_ready import wait_for_database
 
 config = context.config
 if config.config_file_name is not None:
@@ -32,6 +33,7 @@ def do_run_migrations(connection):
 
 
 async def run_async_migrations() -> None:
+    await wait_for_database(Config.DATABASE_URL)
     engine = create_async_engine(Config.DATABASE_URL)
     async with engine.connect() as connection:
         await connection.run_sync(do_run_migrations)