feat(embeds): add TikTok, Twitch, Dailymotion, Streamable, Spotify, SoundCloud players

Generalize the inline-embed system: parseMediaEmbed() resolves any supported URL
to an embed spec (provider + kind + embed URL), and a single MediaEmbedCard
renders the media-forward click-to-play facade for all of them — landscape 16:9
(YouTube, Vimeo, Dailymotion, Streamable, Twitch), portrait 9:16 (Shorts, TikTok),
and short fixed-height audio players (Spotify, SoundCloud). Same privacy facade as
before: nothing loads from the third party until the user presses play, gated by
the 'Inline Media Players' setting.

Twitch embeds pass the current page hostname as the required parent param.
Non-embeddable fallbacks (e.g. vm.tiktok.com short links, non-media tweets) keep
their existing rich OG cards; X/Twitter intentionally keeps its rich tweet card.

All parsers/builders are pure + unit-tested (videoEmbed.test.ts, 10 cases).
Desktop Tauri CSP frame-src updated for the new hosts (separate commit).

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

src/app/features/settings/general/General.tsx

@@ -2348,7 +2348,7 @@ function Messages() {
       <SequenceCard className={SequenceCardStyle} variant="SurfaceVariant" direction="Column">
         <SettingTile
           title="Inline Media Players"
-          description="Play YouTube and Vimeo links right in the chat. Nothing loads from the video site until you press play."
+          description="Play YouTube, Vimeo, TikTok, Twitch, Spotify and more right in the chat. Nothing loads from the third-party site until you press play."
           after={
             <Switch variant="Primary" value={inlineMediaEmbeds} onChange={setInlineMediaEmbeds} />
           }