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.

src/langbot/pkg/persistence/alembic/versions/0006_normalize_mcp_remote_mode.py

@@ -31,9 +31,7 @@ def upgrade() -> None:
     inspector = sa.inspect(conn)
     if 'mcp_servers' not in inspector.get_table_names():
         return
-    conn.execute(
-        sa.text("UPDATE mcp_servers SET mode = 'remote' WHERE mode IN ('sse', 'http')")
-    )
+    conn.execute(sa.text("UPDATE mcp_servers SET mode = 'remote' WHERE mode IN ('sse', 'http')"))
 
 
 def downgrade() -> None:
@@ -46,6 +44,4 @@ def downgrade() -> None:
     inspector = sa.inspect(conn)
     if 'mcp_servers' not in inspector.get_table_names():
         return
-    conn.execute(
-        sa.text("UPDATE mcp_servers SET mode = 'http' WHERE mode = 'remote'")
-    )
+    conn.execute(sa.text("UPDATE mcp_servers SET mode = 'http' WHERE mode = 'remote'"))

src/langbot/pkg/provider/tools/loaders/mcp.py

@@ -191,9 +191,7 @@ class RuntimeMCPSession:
         try:
             await self.exit_stack.aclose()
         except Exception as cleanup_err:
-            self.ap.logger.debug(
-                f'MCP server {self.server_name}: error cleaning up before SSE fallback: {cleanup_err}'
-            )
+            self.ap.logger.debug(f'MCP server {self.server_name}: error cleaning up before SSE fallback: {cleanup_err}')
         self.exit_stack = AsyncExitStack()
         self.session = None