Capture YouTube titles from Discord's embed cache

CURRENT.md

@@ -40,6 +40,15 @@ mobile draft at 390px.
   - [x] C11 preview caching: Discord-hosted image/GIF previews (WebP 320px, hash-addressed, 5 MiB
     cap, one attempt) run after every walk in both modes. Live run `...-20260916090722`:
     `previewed: 2`; thumbs served over `/api/media/<scrape>/<item>/thumb` (200).
+  - [x] C58 Titles from Discord's embed cache. Gone YouTube videos have no oEmbed answer, but
+    Discord keeps the embed title (and, with the rebuilt core bundle, the author/channel). The
+    title lane now asks the source message's embed first and only then the provider oEmbed; the
+    core maps `authorName` from `embed.author.name`, extraction stores it as `title_author`, and
+    the viewer shows a prominent title/channel heading plus "Video unavailable (removed or
+    private)" when a YouTube row has neither. The 783 title errors were reset and the lane
+    backfilled them: the reported example (message 703788394337009754) now reads "Gun Test: Firing
+    Empty Shell's Handheld XM556 Microgun". The channel name populates after the Vesktop client
+    restarts on the new bundle (the client is externally started).
   - [x] C57 Page mode. The media grid has an Infinite/Page flippy toggle in the bar. Page mode
     renders one `pageSize` slice via `offset = (page-1)*pageSize`, shows Prev / editable page
     number / total / Next, persists the page in localStorage, and scrolls to the next page one at