Add version display in footer

- Add version state tracking for demo and server versions
- Create loadVersions() function to fetch server version via API
- Update footer to display both demo version and server version
- Update vite.config.js to inject git commit hash as VITE_VERSION

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

vite.config.js

@@ -1,5 +1,14 @@
 import { defineConfig } from 'vite';
 import react from '@vitejs/plugin-react';
+import { execSync } from 'child_process';
+
+// Get git commit hash
+let version = 'unknown';
+try {
+  version = execSync('git rev-parse --short HEAD', { encoding: 'utf8' }).trim();
+} catch (err) {
+  console.warn('Could not get git commit hash, using "unknown"');
+}
 
 export default defineConfig({
   plugins: [react()],
@@ -10,5 +19,8 @@ export default defineConfig({
   build: {
     outDir: 'dist',
     sourcemap: true
+  },
+  define: {
+    'import.meta.env.VITE_VERSION': JSON.stringify(version)
   }
 });