feat: Search pagination and UX improvements

- Add pagination support to search (previously limited to 50 results)
- Search now scoped to current mailbox/folder
- Support shared mailbox folders in search
- Display total results count (e.g., "50 of 1400 conversations")
- Add clear (X) button to search input
- Re-run search when changing folders during active search
- Remove unused sidebar screenshot

README.md

@@ -183,14 +183,6 @@ npm start
 **Settings**
 <img src="screenshots/06-settings.png" width="100%" alt="Settings">
 
-</td>
-</tr>
-<tr>
-<td colspan="2">
-
-**Sidebar Navigation**
-<img src="screenshots/07-inbox-sidebar.png" width="50%" alt="Sidebar">
-
 </td>
 </tr>
 </table>