feat(embeds): inline YouTube/Vimeo players + media-forward video tiles

Video link tiles (YouTube, Shorts, Vimeo) now play in place instead of only
opening a browser tab. Adds a media-forward 16:9 (9:16 for Shorts) tile with a
privacy-friendly click-to-play facade: the homeserver's cached og:image thumbnail
+ a play button, and only on click does it swap in the cookie-less
youtube-nocookie / player.vimeo iframe — so nothing loads from Google/Vimeo until
the user presses play. Gated by a new 'Inline Media Players' setting (default on);
when off it falls back to a link that opens the video in a new tab.

Also sources YouTube thumbnails from the homeserver og:image instead of
img.youtube.com, which fixes the existing broken YouTube thumbnails on the web
build (nginx img-src has no YouTube host) and removes the pre-click Google request.

Pure URL parsing + embed-URL building moved to utils/videoEmbed.ts (unit-tested).

Note: the desktop app's Tauri CSP frame-src must allow the video hosts (separate
commit in cinny-desktop).

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

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

@@ -2250,6 +2250,7 @@ function Messages() {
   const [mediaAutoLoad, setMediaAutoLoad] = useSetting(settingsAtom, 'mediaAutoLoad');
   const [urlPreview, setUrlPreview] = useSetting(settingsAtom, 'urlPreview');
   const [encUrlPreview, setEncUrlPreview] = useSetting(settingsAtom, 'encUrlPreview');
+  const [inlineMediaEmbeds, setInlineMediaEmbeds] = useSetting(settingsAtom, 'inlineMediaEmbeds');
   const [showHiddenEvents, setShowHiddenEvents] = useSetting(settingsAtom, 'showHiddenEvents');
   const [enforceRetentionLocally, setEnforceRetentionLocally] = useSetting(
     settingsAtom,
@@ -2344,6 +2345,15 @@ function Messages() {
           after={<Switch variant="Primary" value={encUrlPreview} onChange={setEncUrlPreview} />}
         />
       </SequenceCard>
+      <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."
+          after={
+            <Switch variant="Primary" value={inlineMediaEmbeds} onChange={setInlineMediaEmbeds} />
+          }
+        />
+      </SequenceCard>
       <SequenceCard className={SequenceCardStyle} variant="SurfaceVariant" direction="Column">
         <SettingTile
           title="Show Hidden Events"