Fix alembic env crashing on URL-encoded password characters

Passing the DB URL through config.set_main_option() runs it through
ConfigParser, which treats '%' as interpolation syntax — so any password
character that URL-encodes to %xx ('!', '@', '#', ...) crashed migrations
('invalid interpolation syntax'). Build the engine directly from the URL
instead of routing it through the ini config.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/alembic/env.py

@@ -1,7 +1,7 @@
 from logging.config import fileConfig
 
 from alembic import context
-from sqlalchemy import engine_from_config, pool
+from sqlalchemy import create_engine, pool
 
 from app.config import get_settings
 from app.models import Base
@@ -10,13 +10,15 @@ config = context.config
 if config.config_file_name is not None:
     fileConfig(config.config_file_name)
 
-config.set_main_option("sqlalchemy.url", get_settings().sync_database_url)
+# The database URL is passed directly to SQLAlchemy rather than through
+# config.set_main_option(): ConfigParser treats '%' as interpolation syntax,
+# so URL-encoded password characters (e.g. '!' -> '%21') would blow up.
 target_metadata = Base.metadata
 
 
 def run_migrations_offline() -> None:
     context.configure(
-        url=config.get_main_option("sqlalchemy.url"),
+        url=get_settings().sync_database_url,
         target_metadata=target_metadata,
         literal_binds=True,
         dialect_opts={"paramstyle": "named"},
@@ -26,15 +28,14 @@ def run_migrations_offline() -> None:
 
 
 def run_migrations_online() -> None:
-    connectable = engine_from_config(
-        config.get_section(config.config_ini_section, {}),
-        prefix="sqlalchemy.",
-        poolclass=pool.NullPool,
+    connectable = create_engine(
+        get_settings().sync_database_url, poolclass=pool.NullPool
     )
     with connectable.connect() as connection:
         context.configure(connection=connection, target_metadata=target_metadata)
         with context.begin_transaction():
             context.run_migrations()
+    connectable.dispose()
 
 
 if context.is_offline_mode():