fix: use SYNC_DATABASE_URL env var for alembic migrations

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/alembic/env.py

@@ -1,3 +1,4 @@
+import os
 from logging.config import fileConfig
 
 from alembic import context
@@ -9,6 +10,10 @@ config = context.config
 fileConfig(config.config_file_name)
 target_metadata = Base.metadata
 
+# Use SYNC_DATABASE_URL env var if set, otherwise fall back to alembic.ini
+if os.getenv("SYNC_DATABASE_URL"):
+    config.set_main_option("sqlalchemy.url", os.getenv("SYNC_DATABASE_URL"))
+
 
 def run_migrations_offline():
     url = config.get_main_option("sqlalchemy.url")