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.

frontend/vite.config.ts

@@ -2,6 +2,11 @@ import { defineConfig, loadEnv } from 'vite'
 import solid from 'vite-plugin-solid'
 import UnoCSS from 'unocss/vite'
 import path from 'path'
+import { readFileSync } from 'fs'
+
+// Read version from package.json
+const packageJson = JSON.parse(readFileSync(path.resolve(__dirname, './package.json'), 'utf8'))
+const version = packageJson.version
 
 export default defineConfig(({ mode }) => {
   // Load env file from parent directory
@@ -9,6 +14,10 @@ export default defineConfig(({ mode }) => {
   
   return {
     plugins: [solid(), UnoCSS()],
+    define: {
+      // Make version available at build time
+      __APP_VERSION__: JSON.stringify(version)
+    },
     resolve: {
       alias: {
         '@': path.resolve(__dirname, './src'),