feat: 添加 PWA 支持，可添加到手机主屏幕作为独立应用使用

web/public/favicon.svg

@@ -0,0 +1,13 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
+  <rect width="512" height="512" rx="96" fill="#08080d"/>
+  <g transform="translate(256,232)">
+    <!-- Mic body -->
+    <rect x="-48" y="-100" width="96" height="160" rx="48" fill="#6366f1"/>
+    <!-- Mic arc -->
+    <path d="M-72,30 a72,72 0 0,0 144,0" fill="none" stroke="#6366f1" stroke-width="16" stroke-linecap="round"/>
+    <!-- Mic stem -->
+    <line x1="0" y1="102" x2="0" y2="148" stroke="#6366f1" stroke-width="16" stroke-linecap="round"/>
+    <!-- Mic base -->
+    <line x1="-36" y1="148" x2="36" y2="148" stroke="#6366f1" stroke-width="16" stroke-linecap="round"/>
+  </g>
+</svg>