feat: group multi-browser output by source

- Add browser source grouping metadata to SDK-created tabs, groups,
  list results, and aggregate count results.
- Render grouped local/remote browser tables consistently for clients,
  tabs, groups, windows, sessions, and remote status output.
- Document remote control, auth, HTTP gateway usage, and the refreshed
  project structure in the README.
- Add coverage for grouped output and BrowserCounts browser_groups.
- Bump the Python package, extension manifest, and lockfile to 0.15.6.
- Add a just publish helper for building and publishing release artifacts.

browser_cli/sdk/routing.py

@@ -126,7 +126,12 @@ class RoutingMixin:
     if not multi_results:
       return self._client.dispatch(command, args or {})
     by_browser = {target.display_name: int(count or 0) for target, count in multi_results}
-    return BrowserCounts(total=sum(by_browser.values()), by_browser=by_browser)
+    browser_groups = {
+      target.display_name: target.display_group or "local"
+      for target, _count in multi_results
+      if target.display_group or target.remote is None
+    }
+    return BrowserCounts(total=sum(by_browser.values()), by_browser=by_browser, browser_groups=browser_groups)
 
   def multi_list(self, command: str, args: dict | None, mapper):
     """List command, flattening per-browser results in multi-browser mode.