feat(voice): harden Gemini Live provider integration

server/providers/gemini.js

@@ -0,0 +1,22 @@
+import { createGeminiTokenHandler } from './gemini/realtime.js';
+
+/** Mint constrained Live API credentials; the permanent key stays on Node. */
+function geminiLiveProxy({ annotationGuidance, realtime = {} } = {}) {
+  function install(middlewares) {
+    middlewares.use(
+      '/api/gemini/token',
+      createGeminiTokenHandler({ ...realtime, annotationGuidance }),
+    );
+  }
+  return {
+    name: 'gemini-live-proxy',
+    configureServer(server) {
+      install(server.middlewares);
+    },
+    configurePreviewServer(server) {
+      install(server.middlewares);
+    },
+  };
+}
+
+export { geminiLiveProxy };