feat(frontend): enhance API credentials system and build configuration

Add real API support in demo mode with credential checking, implement build-time version injection from package.json, and refactor update checking with 24-hour caching. Migrate landing page from Vue to Astro with comprehensive UI components including Hero, Features, Benefits, and Tech Stack sections. Update CI/CD workflow with expanded cache paths and security scanner version pinned.

landing/astro.config.mjs

@@ -0,0 +1,21 @@
+import { defineConfig } from 'astro/config';
+import tailwind from '@astrojs/tailwind';
+
+export default defineConfig({
+  site: 'https://trackeep.org',
+  output: 'static',
+  integrations: [
+    tailwind()
+  ],
+  vite: {
+    optimizeDeps: {
+      exclude: ['@astrojs/check']
+    }
+  },
+  markdown: {
+    shikiConfig: {
+      theme: 'github-dark-default',
+      wrap: true
+    }
+  }
+});