feat(extension): group connected tabs into a green Playwright tab group (#1514)

## Summary
- Add `tabGroups` permission to the extension manifest
- When the connect page opens (via action button click or MCP relay
connect), place it into a green tab group titled "Playwright"
- When a tab is connected to an MCP session, add it to the same group
- When the active connection closes, remove the connected tab from the
group via `chrome.tabs.ungroup`
- Add three tests: group assigned to connect page, group shared with
connected tab, and group cleaned up on disconnect

packages/extension/manifest.json

@@ -6,7 +6,8 @@
   "permissions": [
     "debugger",
     "activeTab",
-    "tabs"
+    "tabs",
+    "tabGroups"
   ],
   "host_permissions": [
     "<all_urls>"