fix(11): repair broken color patterns from CSS variable migration

- ChannelSidebar: replace inline color-mix style with Tailwind classes for task discussion icons
- MessageItem: replace broken priority config (color-mix inline) with Tailwind utility classes
- MessageItem: replace broken department badge hex-alpha pattern with Tailwind classes
- automation-config: restore ACCENT/LINE as hex values (used in template literal alpha suffixes)
- desktop-shell-service: set nativeTheme.themeSource to sync Windows title bar with app theme

src/main/desktop-shell-service.ts

@@ -8,6 +8,7 @@ import {
   dialog,
   Menu,
   nativeImage,
+  nativeTheme,
   net,
   protocol,
   session,
@@ -220,6 +221,9 @@ export function createDesktopShellService({
       },
     });
 
+    // Sync native theme with app to ensure Windows title bar matches content
+    nativeTheme.themeSource = "light";
+
     if (isDev && devServerUrl) {
       await mainWindow.loadURL(devServerUrl);
     } else {