Add message links, suspect retries, and Discord preview recovery

CURRENT.md

@@ -40,6 +40,19 @@ 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] C54 Message links, suspect retries, and preview recovery. Items now carry `messageUrl`
+    (from `media_sources` + scrape guild), the viewer shows/copies it instead of the expiring CDN
+    link and opens a fresh stream for View full, YouTube items offer an **Open on YouTube**
+    fallback, and the metadata gained Channel/Scrape/Title (title includes the channel kept from
+    oEmbed, `title_author`). Preview and download HTTP failures on Discord hosts first refresh the
+    URL from the source message and retry; if that fails the row parks as a **suspect** with one
+    delayed retry (50 s, runs after the batch; a batch two-thirds suspect doubles the cooldown,
+    60 s floor). Still-failing rows are **unverified** and skipped by normal passes; the Bot tab
+    shows suspect/unverified counts and a segmented progress bar (cached blue, pending gray,
+    failed red). **Recover Discord previews** is a paused one-shot task that re-fetches every
+    Discord-CDN row closed with an HTTP error across all scrapes (mixed bot/puppet via the
+    existing refresh path) and lands in the task history when done. All 1,208 Discord 404 rows
+    sampled 15/15 recoverable.
   - [x] C53 Title catch-up as its own lane. Titles no longer share the preview batch: a dedicated
     `TitleLane` walks every scrape with a pending title, 100 rows per batch with a 10 s pause
     (hard-coded; it is a one-time catch-up and future titles arrive with the scrape), and takes no