refactor: switch icons from react-icons to Phosphor

Replace react-icons and @radix-ui/react-icons with @phosphor-icons/react
for a consistent icon style across all dashboard panels.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

next.config.ts

@@ -30,7 +30,7 @@ const nextConfig: NextConfig = {
   // * Privacy-first: Disable analytics and telemetry
   productionBrowserSourceMaps: false,
   experimental: {
-    optimizePackageImports: ['react-icons'],
+    optimizePackageImports: ['@phosphor-icons/react'],
   },
   images: {
     remotePatterns: [