feat(pwa): add GitHub octocat favicon and PWA manifest

- Add icon.svg with GitHub octocat logo (dark bg, white icon)
- Add apple-icon.tsx for iOS home screen (180x180 dynamic)
- Add manifest.ts for PWA support with app metadata

Author: ryota-murakami

app/apple-icon.tsx

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+/**
+ * Apple Touch Icon
+ *
+ * Dynamic generation of Apple touch icon using the GitHub octocat logo.
+ * This icon appears when users add the app to their iOS home screen.
+ */
+
+import { ImageResponse } from 'next/og'
+
+export const runtime = 'edge'
+
+export const size = {
+  width: 180,
+  height: 180,
+}
+
+export const contentType = 'image/png'
+
+export default function AppleIcon() {
+  return new ImageResponse(
+    <div
+      style={{
+        width: '100%',
+        height: '100%',
+        display: 'flex',
+        alignItems: 'center',
+        justifyContent: 'center',
+        background: '#1f2328',
+        borderRadius: 32,
+      }}
+    >
+      <svg width="140" height="140" viewBox="0 0 24 24" fill="white">
+        <path
+          fillRule="evenodd"
+          clipRule="evenodd"
+          d="M12 2C6.477 2 2 6.484 2 12.017c0 4.425 2.865 8.18 6.839 9.504.5.092.682-.217.682-.483 0-.237-.008-.868-.013-1.703-2.782.605-3.369-1.343-3.369-1.343-.454-1.158-1.11-1.466-1.11-1.466-.908-.62.069-.608.069-.608 1.003.07 1.531 1.032 1.531 1.032.892 1.53 2.341 1.088 2.91.832.092-.647.35-1.088.636-1.338-2.22-.253-4.555-1.113-4.555-4.951 0-1.093.39-1.988 1.029-2.688-.103-.253-.446-1.272.098-2.65 0 0 .84-.27 2.75 1.026A9.564 9.564 0 0112 6.844c.85.004 1.705.115 2.504.337 1.909-1.296 2.747-1.027 2.747-1.027.546 1.379.202 2.398.1 2.651.64.7 1.028 1.595 1.028 2.688 0 3.848-2.339 4.695-4.566 4.943.359.309.678.92.678 1.855 0 1.338-.012 2.419-.012 2.747 0 .268.18.58.688.482A10.019 10.019 0 0022 12.017C22 6.484 17.522 2 12 2z"
+        />
+      </svg>
+    </div>,
+    {
+      ...size,
+    },
+  )
+}

app/icon.svg

@@ -0,0 +1,27 @@
+/**
+ * Web App Manifest
+ *
+ * PWA configuration for GitBox.
+ * Enables "Add to Home Screen" functionality and PWA features.
+ */
+
+import type { MetadataRoute } from 'next'
+
+export default function manifest(): MetadataRoute.Manifest {
+  return {
+    name: 'GitBox',
+    short_name: 'GitBox',
+    description: 'Manage GitHub repositories in Kanban format',
+    start_url: '/',
+    display: 'standalone',
+    background_color: '#ffffff',
+    theme_color: '#1f2328',
+    icons: [
+      {
+        src: '/icon.svg',
+        sizes: 'any',
+        type: 'image/svg+xml',
+      },
+    ],
+  }
+}