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/index.html

@@ -5,13 +5,13 @@
     <meta name="viewport" content="width=device-width, initial-scale=1.0, viewport-fit=cover" />
     <title>达道Task</title>
     <meta name="description" content="达道Task：任务、工单、知识库，一条道走到底" />
-    <!-- 和 App 内左上角、安卓桌面同一枚图标：三段米白线 + 一点陶土 -->
+    <!-- 和 App 内左上角、安卓桌面同一枚图标：三段浅蓝白线 + 一点亮蓝 -->
     <link
       rel="icon"
-      href="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 64 64'%3E%3Crect width='64' height='64' rx='18' fill='%232F6054'/%3E%3Cg stroke='%23EFF5F3' stroke-width='4' stroke-linecap='round'%3E%3Cpath d='M18 23h28'/%3E%3Cpath d='M18 32h19'/%3E%3Cpath d='M18 41h12'/%3E%3C/g%3E%3Ccircle cx='46' cy='41' r='6' fill='%23C2703D'/%3E%3C/svg%3E"
+      href="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 64 64'%3E%3Crect width='64' height='64' rx='18' fill='%23274B73'/%3E%3Cg stroke='%23EAF3FB' stroke-width='4' stroke-linecap='round'%3E%3Cpath d='M18 23h28'/%3E%3Cpath d='M18 32h19'/%3E%3Cpath d='M18 41h12'/%3E%3C/g%3E%3Ccircle cx='46' cy='41' r='6' fill='%235CA8E8'/%3E%3C/svg%3E"
     />
     <!-- 装到手机主屏之后：状态栏跟品牌色走，iOS 用不透明底图 -->
-    <meta name="theme-color" content="#2f6054" />
+    <meta name="theme-color" content="#274b73" />
     <link rel="apple-touch-icon" href="/icons/apple-touch-icon.png" />
     <meta name="apple-mobile-web-app-capable" content="yes" />
     <meta name="apple-mobile-web-app-title" content="达道Task" />