feat: Refactor Gemini integration and build process

This commit centralizes Gemini API interaction into a new `server.ts` file and removes it from the client-side `geminiService.ts`.
It also updates the build process in `package.json` to use `esbuild` for bundling the server code, enabling a more robust build pipeline.
The `index.html` has been cleaned up by removing unnecessary OneSignal SDK initialization.
Additionally, dev dependencies have been updated, including `esbuild` to version `0.28.0`.
A new `test2.ts` file is added for testing Gemini API connectivity.

package.json

@@ -4,8 +4,9 @@
   "version": "0.0.0",
   "type": "module",
   "scripts": {
-    "dev": "vite --port=3000 --host=0.0.0.0",
-    "build": "vite build",
+    "dev": "tsx server.ts",
+    "build": "vite build && esbuild server.ts --bundle --platform=node --format=cjs --packages=external --sourcemap --outfile=dist/server.cjs",
+    "start": "node dist/server.cjs",
     "preview": "vite preview",
     "clean": "rm -rf dist",
     "lint": "tsc --noEmit"
@@ -39,6 +40,7 @@
     "@types/express": "^4.17.21",
     "@types/node": "^22.14.0",
     "autoprefixer": "^10.4.21",
+    "esbuild": "^0.28.0",
     "eslint": "^10.2.1",
     "tailwindcss": "^4.1.14",
     "ts-node": "^10.9.2",