ci: add ruff lint check for unused imports and variables

Add CI step to detect unused imports (F401) and unused variables (F841)
with ruff. Clean up existing violations:

- Remove unused Consolidator import in agent/__init__.py
- Remove unused re import in agent/loop.py
- Remove unused Path import in channels/feishu.py
- Remove unused ContentRepositoryConfigError import in channels/matrix.py
- Remove unused field and CommandHandler imports in channels/telegram.py
- Remove unused exception variable in channels/weixin.py

nanobot/channels/telegram.py

@@ -6,14 +6,14 @@ import asyncio
 import re
 import time
 import unicodedata
-from dataclasses import dataclass, field
+from dataclasses import dataclass
 from typing import Any, Literal
 
 from loguru import logger
 from pydantic import Field
 from telegram import BotCommand, ReactionTypeEmoji, ReplyParameters, Update
 from telegram.error import BadRequest, NetworkError, TimedOut
-from telegram.ext import Application, CommandHandler, ContextTypes, MessageHandler, filters
+from telegram.ext import Application, ContextTypes, MessageHandler, filters
 from telegram.request import HTTPXRequest
 
 from nanobot.bus.events import OutboundMessage