docs: clarify Python module responsibilities

Rewrite the module-level descriptions for all 28 Python files and remove the obsolete integration note from grok_register_ttk.py. Verified on Python 3.9 and Python 3.12.

cpa_xai/oauth_device.py

@@ -1,4 +1,4 @@
-"""xAI OAuth device-code flow for Build/CLI credentials."""
+"""实现 OAuth Device Authorization 的发现、启动和 token 轮询。"""
 
 import json
 import time