Update dependencies and project configuration

Add Nix flake support, update .gitignore to ignore SSL certs, upgrade
@types/bun and TypeScript versions, and update frontend SDK URLs in
index.html and sw.js to new API endpoints

package.json

@@ -8,7 +8,7 @@
     "start": "bun run dev"
   },
   "devDependencies": {
-    "@types/bun": "latest"
+    "@types/bun": "1.3.6"
   },
   "peerDependencies": {
     "typescript": "^5.9.2"