feat(branding): add unified Pipu Music app icons

apps/web/public/favicon.svg

@@ -1 +1,17 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><defs><radialGradient id="g" cx="35%" cy="30%" r="75%"><stop offset="0" stop-color="#9CC6FF"/><stop offset=".55" stop-color="#2F80FF"/><stop offset="1" stop-color="#3A1FA8"/></radialGradient></defs><circle cx="16" cy="16" r="14" fill="url(#g)"/></svg>
+<svg xmlns="http://www.w3.org/2000/svg" width="512" height="512" viewBox="0 0 512 512">
+  <defs>
+    <radialGradient id="orb" cx="28%" cy="18%" r="95%">
+      <stop stop-color="#9CC6FF"/>
+      <stop offset=".42" stop-color="#2F80FF"/>
+      <stop offset=".78" stop-color="#6354E8"/>
+      <stop offset="1" stop-color="#3A1FA8"/>
+    </radialGradient>
+    <linearGradient id="note" x1="0" y1="0" x2=".3" y2="1">
+      <stop stop-color="#FFFFFF"/>
+      <stop offset="1" stop-color="#DFEBFF"/>
+    </linearGradient>
+  </defs>
+  <circle cx="256" cy="256" r="240" fill="url(#orb)"/>
+  <path d="M208 348V164H270C356 164 356 280 270 280H208" fill="none" stroke="url(#note)" stroke-width="44" stroke-linecap="round" stroke-linejoin="round"/>
+  <ellipse cx="181" cy="348" rx="49" ry="36" fill="url(#note)" transform="rotate(-18 181 348)"/>
+</svg>