feat(hub): draw an actual CD for covers with no art, not a flat icon

The monochrome disc icon from the previous commit read as placeholder
UI chrome, not as artwork - too plain for something that is, for most
tiles in a real library, the default look of the grid.

- DiscPlaceholder (music-app.js): a small inline SVG illustration -
  dark disc base, an iridescent radial-gradient sheen mimicking the
  rainbow reflection a real CD's data side has, two faint groove
  rings, a light label ring, a dark spindle hole. Each instance gets
  its own gradient id (a module-level counter) rather than one literal
  id repeated - a grid renders many of these at once, and a shared id
  would leave every disc after the first pointing at whichever
  <radialGradient> the browser happened to resolve.
- AlbumCard and MusicDetailModal now branch on coverHash directly:
  MediaThumb (the real chunk-path image) when there is one,
  DiscPlaceholder when there isn't - rather than routing "no cover"
  through MediaThumb's own generic small-icon fallback, which is still
  right for its other callers (list rows, Videos).
- icon.js: the flat monochrome "disc" icon this replaces is removed -
  nothing else used it.
- style.css: .music-disc-empty/.music-disc-svg replace the old
  .video-thumb-empty overrides; still sized relative to the tile (82%)
  so it scales with .music-grid's auto-fill columns.

Client-side only. npm run sync-ui re-run. Full suite: 1129 passed, no
regressions.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KBi7ALLGfwcjBXt57yNMcy

1 files changed, 18 insertions, 14 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/style.css b/packages/meshbay-hub/src/meshbay_hub/static/style.css
index 6c3c0f6..3d411f7 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/style.css
+++ b/packages/meshbay-hub/src/meshbay_hub/static/style.css
@@ -2726,17 +2726,19 @@ a.transfer-name {
   display: block;
   background: var(--bg-surface);
 }
-.music-cover.video-thumb-empty { aspect-ratio: 1 / 1; }
-/* A big, plain disc rather than the small note icon shared with list rows —
-   most tiles land here (few files carry embedded/sibling art), so this is
-   the default look of the grid, not a rare fallback; it needs to read as
-   deliberate, not broken. Sized relative to the tile so it scales with
-   .music-grid's auto-fill columns instead of one fixed px value. */
-.music-cover.video-thumb-empty .icon {
-  width: 55%;
-  height: 55%;
-  color: var(--text-dim);
+/* The drawn-CD placeholder (DiscPlaceholder, music-app.js) — sized relative
+   to the tile so it scales with .music-grid's auto-fill columns instead of
+   one fixed px value, and never clipped by the square tile's own overflow. */
+.music-disc-empty {
+  width: 100%;
+  aspect-ratio: 1 / 1;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  background: var(--bg-surface);
+  overflow: hidden;
 }
+.music-disc-svg { width: 82%; height: 82%; }
 
 .music-card-info { padding: 8px 10px; }
 .music-card-title {
@@ -2792,10 +2794,12 @@ a.transfer-name {
   flex-shrink: 0;
   background: var(--bg-raised);
 }
-.music-detail-cover.video-thumb-empty .icon {
-  width: 55%;
-  height: 55%;
-  color: var(--text-dim);
+.music-detail-cover.music-disc-empty {
+  width: 96px;
+  height: 96px;
+  border-radius: 6px;
+  flex-shrink: 0;
+  background: var(--bg-raised);
 }
 .music-detail-meta { min-width: 0; }
 .music-detail-artist { font-weight: 600; font-size: 0.95em; }