refactor(pages): one about page per language, no R2 cache by default

- app/[lang]/about/page.tsx renders en, zh and ja (zh-Hant falls back
  to zh) from one JSX tree with per-language texts and generateMetadata;
  delete the cn/ and ja/ copies and redirect their old URLs
- app/[lang]/layout.tsx: use hasLocale, an OG locale table, and real
  zh/ja title and description
- components/icons/github.tsx replaces react-icons and lucide's
  deprecated Github icon
- quota-limit-toast: read the dictionary keys directly, shadow-float
- Cloudflare: defineCloudflareConfig({}) without R2, no r2_buckets, no
  dev-time OpenNext init, cf-typegen script removed,
  @opennextjs/cloudflare moves to devDependencies, docs updated

components/icons/github.tsx

@@ -0,0 +1,13 @@
+// GitHub mark as an inline SVG, so no icon package is needed for one icon
+export function GitHubIcon({ className }: { className?: string }) {
+    return (
+        <svg
+            viewBox="0 0 16 16"
+            fill="currentColor"
+            aria-hidden="true"
+            className={className}
+        >
+            <path d="M8 0C3.58 0 0 3.58 0 8c0 3.54 2.29 6.53 5.47 7.59.4.07.55-.17.55-.38 0-.19-.01-.82-.01-1.49-2.01.37-2.53-.49-2.69-.94-.09-.23-.48-.94-.82-1.13-.28-.15-.68-.52-.01-.53.63-.01 1.08.58 1.23.82.72 1.21 1.87.87 2.33.66.07-.52.28-.87.51-1.07-1.78-.2-3.64-.89-3.64-3.95 0-.87.31-1.59.82-2.15-.08-.2-.36-1.02.08-2.12 0 0 .67-.21 2.2.82.64-.18 1.32-.27 2-.27.68 0 1.36.09 2 .27 1.53-1.04 2.2-.82 2.2-.82.44 1.1.16 1.92.08 2.12.51.56.82 1.27.82 2.15 0 3.07-1.87 3.75-3.65 3.95.29.25.54.73.54 1.48 0 1.07-.01 1.93-.01 2.2 0 .21.15.46.55.38A8.013 8.013 0 0016 8c0-4.42-3.58-8-8-8z" />
+        </svg>
+    )
+}