ci: switch syntax-check from cli.py to cli/ package

The CLI was split into a package in b5a44a1; the workflow still
ran ``python -m py_compile cli.py`` against the now-renamed file
and failed with "No such file or directory: 'cli.py'".

Use ``python -m compileall -q cli`` so every module under the
package (``main.py``, ``_legacy.py``, ``commands/``, ``components/``,
``utils/``, ``_version.py``, ``__main__.py``) is checked together.

.github/workflows/test.yml

@@ -25,7 +25,7 @@ jobs:
       - name: Syntax check
         run: |
           cd agent
-          python -m py_compile cli.py
+          python -m compileall -q cli
           python -m py_compile api_server.py
           python -m py_compile mcp_server.py
           python -m py_compile src/agent/loop.py