fix: Use proper Unicode treble clef (𝄞) for album art placeholders

Replaces broken SVG path with Unicode U+1D11E treble clef symbol
rendered via SVG text element. Applied to all three locations:
- Gallery ribbon: small treble clef (5x5)
- Gallery tile: medium treble clef (10x10)
- DetailPanel: large treble clef (14x14)

frontend/src/components/DetailPanel.tsx

@@ -120,8 +120,8 @@ export default function DetailPanel({ clip, onClose, onRename, onDelete, onUploa
               />
             ) : (
               <div className="w-full aspect-square bg-white/5 rounded-lg flex flex-col items-center justify-center text-lyria-accent/20">
-                <svg className="w-14 h-14" viewBox="0 0 24 24" fill="currentColor">
-                  <path d="M11.5 2c-.28 0-.5.22-.5.5v8.17c-.94-.42-2.08-.37-3.06.2C7.06 11.39 6.3 12.7 6.5 14.1c.2 1.4 1.3 2.48 2.7 2.72.67.12 1.37.04 2.01-.21.35-.14.65-.34.9-.6.14-.14.26-.3.37-.47l.02.02V21.5c0 .28.22.5.5.5s.5-.22.5-.5V5.3c.67.4 1.5.7 2.5.7 2.21 0 4-1.79 4-4h-1c0 1.66-1.34 3-3 3-.94 0-1.78-.44-2.5-1.2V2.5c0-.28-.22-.5-.5-.5zM9.5 11.5c.53 0 1.03.2 1.5.54v4.92c-.47.34-.97.54-1.5.54-1.38 0-2.5-1.12-2.5-2.5s1.12-2.5 2.5-2.5z"/>
+                <svg className="w-14 h-14" viewBox="0 0 24 24">
+                  <text x="12" y="19" textAnchor="middle" fontSize="20" fill="currentColor">𝄞</text>
                 </svg>
                 <span className="text-xs mt-1 text-lyria-muted/40">No album art</span>
               </div>