fix(11-01): add mode column to test database schema

- Add mode column to agents table in test-helpers CREATE_TABLES_SQL
- Generate drizzle migration for mode column

src/db/repositories/drizzle/test-helpers.ts

@@ -79,6 +79,7 @@ CREATE TABLE IF NOT EXISTS agents (
   session_id TEXT,
   worktree_id TEXT NOT NULL,
   status TEXT NOT NULL DEFAULT 'idle',
+  mode TEXT NOT NULL DEFAULT 'execute',
   created_at INTEGER NOT NULL,
   updated_at INTEGER NOT NULL
 );