* feat(app): add persistent workspace side panes
Keep the common review and file-browsing workflow beside the active agent without tearing down pane contents. Workspace tabs now share one compact chip language, assistant file links route into the retained right pane, and diff/file trees share stable geometry.
* fix(app): localize pull request empty state
* test(app): update explorer pane coverage
* fix(app): preserve explorer pane workflows
* test(app): make explorer tab selection idempotent
* fix(app): persist workspace review pins
* fix(app): preserve sidebar scrim drag hook
* fix(app): restore companion pane interactions
* test(app): follow selected sidebar surface
