refactor(structure): reorganize app layout

BREAKING CHANGE: root backend/frontend directories and old run/manage entrypoints were removed. Use apps/backend, apps/frontend, and python main.py commands instead.

apps/frontend/public/favicon.svg

@@ -0,0 +1,20 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
+  <!-- 圆形绿色渐变背景 -->
+  <defs>
+    <linearGradient id="greenGradient" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" style="stop-color:#66bb6a;stop-opacity:1" />
+      <stop offset="100%" style="stop-color:#4caf50;stop-opacity:1" />
+    </linearGradient>
+  </defs>
+
+  <!-- 圆形背景 -->
+  <circle cx="50" cy="50" r="48" fill="url(#greenGradient)"/>
+
+  <!-- 白色打钩图标 -->
+  <path d="M 30 50 L 42 62 L 70 34"
+        stroke="white"
+        stroke-width="8"
+        stroke-linecap="round"
+        stroke-linejoin="round"
+        fill="none"/>
+</svg>