fix(extension): add "tabs" permission for live tab awareness off-localhost

Without the `tabs` permission, chrome.tabs.query() returns tab objects with
undefined url/title for any site outside host_permissions (i.e. everything
except 127.0.0.1). snapshotTabs then wrote empty strings into tabs.json and
active-tab.json silently skipped writes, and the sidebar agent lost track
of what page the user was actually on. activeTab is too narrow — it only
applies after a user gesture on the extension action, not for background
polling.

Manifest test asserts permissions includes 'tabs' so future drift is caught.

Note: this widens the extension's permission surface; users will see the
broader scope on next install. Called out in the CHANGELOG.

Contributed by @fredchu (#1257).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

extension/manifest.json

@@ -3,7 +3,7 @@
   "name": "gstack browse",
   "version": "0.1.0",
   "description": "Live activity feed and @ref overlays for gstack browse",
-  "permissions": ["sidePanel", "storage", "activeTab", "scripting"],
+  "permissions": ["sidePanel", "storage", "activeTab", "scripting", "tabs"],
   "host_permissions": ["http://127.0.0.1:*/", "ws://127.0.0.1:*/"],
   "action": {
     "default_icon": {