fix: make alembic migration mandatory — fail deploy if migration fails

Removed silent fallback that was hiding migration failures.

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

docker/backend/entrypoint.sh

@@ -42,7 +42,8 @@ except:
 
     # Run database migrations
     echo "📦 Running database migrations..."
-    alembic upgrade head || echo "⚠️  Migration skipped (may already be up to date)"
+    alembic upgrade head
+    echo "✅ Migrations applied successfully"
 fi
 
 # Wait for Redis if configured