feat(ui): add multi-session selection and deletion (#51924)

* feat(sessions): implement multi-session deletion and selection functionality

- Added `deleteSessionsAndRefresh` function to handle deletion of multiple sessions.
- Updated session state management to track selected session keys.
- Enhanced UI to support bulk actions for selected sessions, including delete and unselect options.
- Refactored related tests to accommodate new multi-session deletion logic.
- Improved responsiveness of sessions table with new CSS rules for mobile layouts.

* feat(sessions): add page deselection functionality and enhance error handling

- Implemented `onDeselectPage` method to allow deselecting specific pages in the session view.
- Updated `deleteSessionsAndRefresh` to handle multiple deletion errors, storing them in an array and displaying a consolidated error message.
- Enhanced tests to verify the new deselection behavior and updated error handling for session deletions.

vitest.config.ts

@@ -49,6 +49,7 @@ export default defineConfig({
       "ui/src/ui/controllers/agents.test.ts",
       "ui/src/ui/controllers/chat.test.ts",
       "ui/src/ui/controllers/sessions.test.ts",
+      "ui/src/ui/views/sessions.test.ts",
       "ui/src/ui/app-gateway.sessions.node.test.ts",
     ],
     setupFiles: ["test/setup.ts"],