fix(messages): list_messages never calls get_media_label

[PathKnower]

Summary

• list_messages builds its own record dict directly from msg.message, without the get_media_label(msg) fallback that message_to_dict (used by get_history) already has.
• Net effect: a voice message, photo, sticker, or any other captionless media item shows up in list_messages output looking identical to an actually-empty message — no media field, no indication anything was attached.
• Fix adds the same one-line get_media_label call message_to_dict already does, so list_messages records get a media field (e.g. "media": "voice", "media": "photo") whenever the message carries media, whether or not there's a caption.

Test plan

uv run pytest tests/ -q
# 281 passed

uv run pre-commit run --files telegram_mcp/tools/messages.py
black....................................................................Passed
flake8...................................................................Passed

Manually confirmed against a real chat with several voice/photo messages via a running server — list_messages now reports "media": "voice" for a voice message that previously showed no media indicator at all.