feat: 全面优化 SEO 元数据、结构化数据和站点地图

为所有工具页面添加 canonical URL、keywords、SoftwareApplication 和
BreadcrumbList 结构化数据，优化标题和描述以包含搜索意图关键词，
更新站点地图日期和优先级，移除无效的 SearchAction，新增 PWA manifest。

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

public/manifest.json

@@ -0,0 +1,16 @@
+{
+  "name": "KYMR.TOP - Game Asset Tools",
+  "short_name": "KYMR.TOP",
+  "description": "Free online tools for game developers. Compress images, extract video frames, optimize audio, generate texture atlases. Browser-based, privacy-first.",
+  "start_url": "/",
+  "display": "standalone",
+  "background_color": "#09090b",
+  "theme_color": "#09090b",
+  "icons": [
+    {
+      "src": "/icon.svg",
+      "sizes": "any",
+      "type": "image/svg+xml"
+    }
+  ]
+}