Fix Antigravity model list and enhance clipboard-guided handoff UX

public/index.html

@@ -936,6 +936,10 @@
 
         <div id="dev-handoff-result-box" class="nb-edit-box hidden"></div>
 
+        <div id="dev-handoff-instruction-note" class="muted-label" style="font-size:0.8rem; padding:0.4rem 0.6rem; background:rgba(76,140,245,0.08); border-radius:6px; border-left:3px solid var(--accent-primary); margin-top:0.4rem;">
+          🛸 Submitting switches focus to Antigravity and copies the complete project specification to your clipboard. Simply press <kbd>Ctrl+V</kbd> in Antigravity's chat to start coding.
+        </div>
+
         <div class="modal-footer">
           <button type="button" id="btn-cancel-dev-modal" class="btn btn-ghost">Cancel</button>
           <button type="submit" id="btn-submit-dev-handoff" class="btn btn-primary">