fix(mcp): ruff format remote-mode files; make migration head test revision-agnostic

CI follow-up to the local/remote MCP work:

- Apply ruff format to provider/tools/loaders/mcp.py and the 0006
  normalize-remote-mode migration (Lint job failed on formatting).
- test_migrations.py hardcoded the head revision as 0005_*, which broke
  once 0006 landed. Resolve the actual head from the Alembic
  ScriptDirectory so future migrations don't require editing the test.

tests/integration/persistence/test_migrations.py

@@ -17,7 +17,21 @@ from langbot.pkg.persistence.alembic_runner import (
     run_alembic_upgrade,
     run_alembic_stamp,
     get_alembic_current,
+    _ALEMBIC_DIR,
 )
+from alembic.config import Config
+from alembic.script import ScriptDirectory
+
+
+def _get_script_head() -> str:
+    """Resolve the current Alembic head revision from the script directory.
+
+    Avoids hardcoding a revision number in assertions so adding a new
+    migration doesn't require editing the migration tests.
+    """
+    cfg = Config()
+    cfg.set_main_option('script_location', _ALEMBIC_DIR)
+    return ScriptDirectory.from_config(cfg).get_current_head()
 
 
 pytestmark = pytest.mark.integration
@@ -103,8 +117,10 @@ class TestSQLiteMigrationUpgrade:
         # Verify revision
         rev = await get_alembic_current(sqlite_engine)
         assert rev is not None, 'Expected a revision after upgrade'
-        # Head should be the latest migration
-        assert rev.startswith('0005'), f'Expected head to be 0005_*, got {rev}'
+        # Head should be the latest migration. Resolve the actual head from the
+        # Alembic script directory instead of hardcoding a revision number, so
+        # adding a new migration doesn't require editing this assertion.
+        assert rev == _get_script_head(), f'Expected head {_get_script_head()}, got {rev}'
 
     @pytest.mark.asyncio
     async def test_upgrade_idempotent(self, sqlite_engine):