Mobile responsiveness for source picker, aura, and library empty CTA

The new components shipped this PR (source icon row, fallback banner,
glow aura, library-empty search CTA) had no responsive styling. On
phones the rows ran fine via horizontal scroll but the chips wasted a
lot of space per icon, the CTA could overflow on narrow screens, and
the aura kept its desktop-sized ellipse for no benefit.

At ≤768px (tablet/phone):
- Enhanced source row: tighter padding, 24x24 glyphs, 72px chip
  min-width.
- Global widget source row: even tighter, 20x20 glyphs, 62px chips.
- Fallback banners scale down to match.
- Aura shrinks to a 440x160 / 540x200 ellipse and a 180px-tall strip
  so it doesn't eat short mobile viewports.
- Library empty CTA allows text wrap + reduced padding so the
  "Search online for "long artist name"" string doesn't break the
  layout on narrow screens.

At ≤480px (phone):
- Enhanced chips drop to 44px min-width.
- Global widget chips drop to 40px.
- Both hide the source-name label, showing icon + tooltip only — the
  full 8-source row now fits or scrolls minimally at that scale.
- Aura narrows further to 140px tall.
- Library CTA nudges down to 12px font.

webui/static/mobile.css

@@ -3627,4 +3627,119 @@
         width: calc(100vw - 16px);
         bottom: 54px;
     }
+}
+
+/* ─────────────────────────────────────────────────────────────
+   Source picker row — Search page + global widget responsive.
+   Chips shrink on tablet, labels drop on phone so the full row
+   of 8 sources remains scannable without hijacking the screen. */
+@media (max-width: 768px) {
+    .enh-source-row {
+        padding: 8px 8px;
+        margin: 8px 0 10px;
+        gap: 6px;
+        border-radius: 12px;
+    }
+    .enh-source-icon {
+        min-width: 72px;
+        padding: 8px 10px;
+        gap: 4px;
+        font-size: 10.5px;
+    }
+    .enh-source-icon-glyph,
+    .enh-source-icon-glyph img {
+        width: 24px;
+        height: 24px;
+    }
+    .enh-source-icon-label { font-size: 10.5px; }
+    .enh-fallback-banner {
+        font-size: 11px;
+        padding: 6px 10px;
+    }
+
+    /* Global widget source row (inside the popover) */
+    .gsearch-source-row {
+        padding: 10px 10px 6px;
+        gap: 4px;
+    }
+    .gsearch-source-icon {
+        min-width: 62px;
+        padding: 6px 8px;
+        gap: 3px;
+    }
+    .gsearch-source-icon-glyph,
+    .gsearch-source-icon-glyph img {
+        width: 20px;
+        height: 20px;
+    }
+    .gsearch-fallback-banner {
+        font-size: 10px;
+        padding: 5px 10px;
+    }
+
+    /* Ambient glow under the global search — trim size so it doesn't
+       dominate a short mobile viewport. */
+    .gsearch-aura {
+        height: 180px;
+        background:
+            radial-gradient(ellipse 440px 160px at 50% 100%,
+                rgba(var(--accent-rgb), 0.20) 0%,
+                rgba(var(--accent-rgb), 0.08) 35%,
+                rgba(var(--accent-rgb), 0.02) 65%,
+                transparent 85%);
+    }
+    .gsearch-aura.active {
+        background:
+            radial-gradient(ellipse 540px 200px at 50% 100%,
+                rgba(var(--accent-rgb), 0.34) 0%,
+                rgba(var(--accent-rgb), 0.14) 28%,
+                rgba(var(--accent-rgb), 0.04) 58%,
+                transparent 85%);
+    }
+
+    /* Library empty-state hand-off CTA — allow wrap on narrow screens
+       so long artist queries don't overflow. */
+    .library-empty-search-cta {
+        flex-wrap: wrap;
+        justify-content: center;
+        padding: 10px 14px;
+        font-size: 13px;
+        max-width: 100%;
+    }
+    .library-empty-search-cta-text {
+        white-space: normal;
+        text-align: center;
+    }
+}
+
+/* Very narrow phones — drop the icon labels entirely and show just the
+   glyphs. Tap target stays big enough, row compacts dramatically. */
+@media (max-width: 480px) {
+    .enh-source-row {
+        padding: 6px 6px;
+        gap: 4px;
+        border-radius: 10px;
+    }
+    .enh-source-icon {
+        min-width: 44px;
+        padding: 6px 8px;
+    }
+    .enh-source-icon-label { display: none; }
+
+    .gsearch-source-row {
+        padding: 8px 8px 5px;
+        gap: 4px;
+    }
+    .gsearch-source-icon {
+        min-width: 40px;
+        padding: 5px 7px;
+    }
+    .gsearch-source-icon-label { display: none; }
+
+    .gsearch-aura { height: 140px; }
+
+    .library-empty-search-cta {
+        font-size: 12px;
+        padding: 9px 12px;
+    }
 }