feat(design): 主色由墨松绿改为景泰蓝蓝系，Logo 与图标同步

纸白底改冷调与主色同轴；语义色 sage/wheat/rust 不变，sky 提亮与主色区分。Logo 三段线改浅蓝白、圆点改亮蓝；favicon/PWA 图标/安卓自适应图标/状态栏一并重绘，新增 tools/make-icons.py 作为唯一出处。

web/src/components/icons.tsx

@@ -290,13 +290,13 @@ export const Spinner = ({ size = 16, className = "" }: { size?: number; classNam
 
 export const Logo = ({ size = 28 }: { size?: number }) => (
   <svg width={size} height={size} viewBox="0 0 32 32" aria-hidden>
-    <rect width="32" height="32" rx="9" fill="#2F6054" />
+    <rect width="32" height="32" rx="9" fill="#274B73" />
     <path
       d="M9 11.5h14M9 16h9.5M9 20.5h6"
-      stroke="#EFF5F3"
+      stroke="#EAF3FB"
       strokeWidth="2"
       strokeLinecap="round"
     />
-    <circle cx="23" cy="20.5" r="3" fill="#C2703D" />
+    <circle cx="23" cy="20.5" r="3" fill="#5CA8E8" />
   </svg>
 );