docs(quick-reference): add lock block action

Added documentation for the lock/unlock block feature (admin only).
Note: Image placeholder added, pending actual screenshot.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: waleedlatif1

apps/docs/content/docs/en/quick-reference/index.mdx

@@ -180,6 +180,11 @@ A quick lookup for everyday actions in the Sim workflow editor. For keyboard sho
       <td>Right-click → **Enable/Disable**</td>
       <td><ActionImage src="/static/quick-reference/disable-block.png" alt="Disable block" /></td>
     </tr>
+    <tr>
+      <td>Lock/Unlock a block</td>
+      <td>Hover block → Click lock icon (Admin only)</td>
+      <td><ActionImage src="/static/quick-reference/lock-block.png" alt="Lock block" /></td>
+    </tr>
     <tr>
       <td>Toggle handle orientation</td>
       <td>Right-click → **Toggle Handles**</td>