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/email/channel.py

@@ -116,7 +116,7 @@ class EmailChannel(Channel, PollingMixin):
             self._imap.login(cfg.imap_username, cfg.imap_password)
             self._imap.select(cfg.imap_mailbox)
         except Exception as e:
-            raise ChannelError(f"IMAP failed: {e}")
+            raise ChannelError(f"IMAP failed: {e}") from e
 
     def _reconnect_imap(self) -> None:
         try: