docs: document inline media embeds feature

- README: new bullet for inline media embeds (video/audio/post players + facade).
- LOTUS_FEATURES: 'Inline Media Embeds' section (kinds table, facade, provider
  notes, sandbox, setting, CSP, the fixed YouTube-thumbnail web bug).
- LOTUS_TODO: awaiting-verification row (16 providers) + deferred providers
  (Bandcamp / on.soundcloud / Vimeo event) under the feature backlog + the iframe
  onError gap.
- LOTUS_TESTING: section Q (facade, TikTok, post self-resize + close, new
  Bluesky/Loom/Kick + toggle + cap).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -41,6 +41,7 @@ The Lotus Chat logo (`public/res/Lotus.png`) is a derivative work based on the o
 - Deleted messages show a placeholder instead of disappearing
 - Code blocks highlight syntax for JS/TS, Python, and Rust
 - Rich link preview cards for YouTube, GitHub, Twitter/X, Reddit, Spotify, Twitch, Steam, Wikipedia, Discord, npm, Stack Overflow, and IMDb
+- Inline media embeds — play videos and posts in place instead of opening a browser tab: YouTube/Shorts, Vimeo, Dailymotion, Streamable, Twitch, Loom, and Kick as video players; TikTok, X/Twitter, Instagram, Reddit, and Bluesky as inline posts; Spotify, SoundCloud, Apple Music, and Tidal as a built-in audio player. A privacy-friendly facade shows the homeserver's cached thumbnail and only loads the third-party player when you press play. Toggle at Settings → General → "Inline Media Players" (on by default)
 
 ### Calls & Voice