Fix duplicate posting, HTML escaping, restore sendRichMessage correctly

- Stop re-sending to a platform that already succeeded when the other
  platform failed (was causing duplicate posts on partial failure)
- Escape VK post text before sending with parse_mode=HTML instead of
  only escaping matched bracket-link substrings (bare & < > broke sends)
- Restore Telegram sendRichMessage (Bot API 10.1) ported faithfully from
  new_vk_parser's proven implementation, with fallback to standard
  send_photo/send_video/send_media_group
- Restore "media unavailable" note when a video/photo fails to download
  instead of silently dropping it
- Handle YouTube link attachments from VK posts (route into yt-dlp)
- MAX: chunk media beyond 10 items into follow-up messages instead of
  dropping them
- yt-dlp format selector no longer falls back to unconstrained height
- Wire up VK_RATE_LIMIT_RPS, drop unused Pillow dep and dead config fields

requirements.txt

@@ -3,5 +3,4 @@ aiohttp==3.12.13
 aiosqlite==0.21.0
 loguru==0.7.3
 pydantic-settings==2.10.1
-Pillow==11.3.0
 yt-dlp>=2026.1.1