feat(admin): per-feed Subscribe chips with copy/open/validate for RSS/Atom/JSON

Replace the stacked RSS/Atom URL rows in the dashboard with a compact
"Subscribe" chip block exposing all three feed formats — including JSON
Feed, previously absent from the admin UI. Each chip carries copy, open,
and validate actions; validation links to the W3C Feed Validator (RSS/Atom)
and validator.jsonfeed.org (JSON). The Table view's RSS+Atom columns fold
into a single Formats column.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/scripts/client/dashboard.ts

@@ -139,14 +139,14 @@ function setupFeedTableResizing(): void {
     title: 220,
     feedId: 120,
     email: 160,
-    rss: 160,
+    formats: 200,
     actions: 160,
   };
   const defaultWidths: Record<string, number> = {
     title: 340,
     feedId: 160,
     email: 220,
-    rss: 220,
+    formats: 230,
     actions: 200,
   };