refactor: simplify Vite config to use unified config as single source

- Remove loadEnv() double-loading in Vite configuration
- Use unifiedConfig directly for all environment variables
- Add additional config variables for better frontend access
- Eliminates configuration conflicts and reduces complexity
- Provides cleaner, more predictable build process

vite.config.ts

@@ -1,20 +1,13 @@
 import path from 'path';
-import { defineConfig, loadEnv } from 'vite';
+import { defineConfig } from 'vite';
 import { unifiedConfig } from './config/unified.config';
 
-export default defineConfig(({ mode }) => {
+export default defineConfig(() => {
-  // Still load env for backward compatibility and overrides
+  // Use unified config as the single source of truth
-  const env = loadEnv(mode, '.', '');
-
-  // Use unified config as the primary source
   const config = unifiedConfig;
 
   return {
     define: {
-      // Legacy API key support
-      'process.env.API_KEY': JSON.stringify(env.GEMINI_API_KEY),
-      'process.env.GEMINI_API_KEY': JSON.stringify(env.GEMINI_API_KEY),
-
       // Application configuration from unified config
       'import.meta.env.VITE_APP_NAME': JSON.stringify(config.app.name),
       'import.meta.env.VITE_APP_VERSION': JSON.stringify(config.app.version),
@@ -71,6 +64,15 @@ export default defineConfig(({ mode }) => {
       'import.meta.env.IS_DEVELOPMENT': JSON.stringify(
         config.app.environment === 'development'
       ),
+
+      // Additional configurations
+      'import.meta.env.VITE_USE_MOCK_DB': JSON.stringify(
+        config.database.useMock
+      ),
+      'import.meta.env.VITE_LOG_LEVEL': JSON.stringify(config.logging.level),
+      'import.meta.env.VITE_ENABLE_MONITORING': JSON.stringify(
+        config.features.enableMonitoring
+      ),
     },
     resolve: {
       alias: {