make Claude sidebar sub-tabs keyboard-activatable

The Activity / Team / Config sub-tabs were built on a raw GestureDetector,
so Tab traversal skipped them and Enter/Space did nothing — a gap against
the repo's a11y contract. Switch to ClideTappable (focusable, Enter/Space
activates) wrapped in button + selected semantics, and add a test that
drives the switch via ActivateIntent rather than a pointer tap.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -58,6 +58,11 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Fixed
 
+- The Claude sidebar's Activity / Team / Config sub-tabs are now keyboard-
+  activatable: they were pointer-only (raw `GestureDetector`), so Tab traversal
+  skipped them and Enter/Space did nothing. They now use `ClideTappable`
+  (focusable, Enter/Space → activate) and carry button + selected semantics.
+  (T-182)
 - The default keymap is no longer silently disabled at startup: `default.yaml`
   bound Tab/Shift+Tab to undefined `focus.next`/`focus.previous` intents, which
   made the loader drop the entire preset (palette, quick-open, find-in-files,