ChatGPT to Gemini exporter, v1.4

A Chrome MV3 extension that exports a full ChatGPT history to JSON in the
shape of ChatGPT's own conversations.json, for the Amgreat Gemini migration
tool. Everything runs in the user's browser against their own session.

Batches of 25 per file, downloaded through the service worker because Chrome
blocks multiple page-initiated downloads. Adaptive pacing with 429 backoff,
Retry-After support, token refresh and localStorage resume.

manifest.json

@@ -0,0 +1,15 @@
+{
+  "manifest_version": 3,
+  "name": "ChatGPT export for Gemini (Amgreat)",
+  "version": "1.4",
+  "description": "Exports your full ChatGPT history to a JSON file for the Amgreat Gemini migration tool. Runs entirely in your own browser; nothing is sent anywhere.",
+  "permissions": ["downloads"],
+  "background": { "service_worker": "background.js" },
+  "content_scripts": [
+    {
+      "matches": ["https://chatgpt.com/*", "https://chat.openai.com/*"],
+      "js": ["content.js"],
+      "run_at": "document_idle"
+    }
+  ]
+}