fix: automatic DB migration — run before backend starts

Three fixes to ensure alembic migrations always run in production:

1. entrypoint.sh: add `exec "$@"` passthrough so `docker compose run
   --rm backend alembic upgrade head` actually runs alembic instead of
   ignoring args and starting uvicorn.

2. entrypoint.sh: remove `|| echo` fallback on alembic — if migration
   fails the container must stop, not silently continue.

3. deploy.yml: start only postgres+redis first, run migration, THEN
   start backend. Previously the backend started before migration,
   ran with stale schema, and the separate migration step was broken
   by the entrypoint bug.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docker/backend/entrypoint.sh

@@ -1,6 +1,12 @@
 #!/bin/bash
 set -e
 
+# If a command is passed (e.g. `docker compose run --rm backend alembic upgrade head`),
+# run it directly instead of the full startup sequence.
+if [ $# -gt 0 ]; then
+    exec "$@"
+fi
+
 echo "🚀 Starting Document Translation API..."
 
 # Wait for database to be ready (if DATABASE_URL is set)
@@ -42,7 +48,7 @@ except:
 
     # Run database migrations
     echo "📦 Running database migrations..."
-    alembic upgrade head || echo "⚠️  Migration skipped (may already be up to date)"
+    alembic upgrade head
 fi
 
 # Wait for Redis if configured