chore: resolve all ruff linting and static analysis errors in EvoScientist/

- Fix RUF006: Implement background task tracking in Discord, iMessage, WeChat, and TUI to prevent premature GC of fire-and-forget tasks.
- Fix B904: Add explicit exception chaining (raise ... from) across all exception handlers.
- Fix RUF012: Annotate mutable class attributes with ClassVar for command arguments and media maps.
- Fix B008: Refactor Typer commands in cli/commands.py to use Annotated for argument and option defaults.
- Fix B023/B018: Resolve late-binding issues in lambdas and remove useless expressions.
- Fix syntax errors in retry.py docstrings and models.py lambda parameter ordering.

EvoScientist/channels/dingtalk/channel.py

@@ -6,6 +6,7 @@ import logging
 from dataclasses import dataclass
 from datetime import datetime
 from pathlib import Path
+from typing import ClassVar
 from urllib.parse import quote_plus
 
 from ..base import Channel, ChannelError, RawIncoming
@@ -319,7 +320,7 @@ class DingTalkChannel(Channel, WebSocketMixin, TokenMixin):
 
     # ── Media send ────────────────────────────────────────────────
 
-    _IMAGE_EXTS = {".jpg", ".jpeg", ".png", ".gif", ".bmp", ".webp"}
+    _IMAGE_EXTS: ClassVar[set[str]] = {".jpg", ".jpeg", ".png", ".gif", ".bmp", ".webp"}
 
     async def _send_media_impl(
         self,