Make plan deletion visible and reliable with in-page confirmation

public/plans.html

@@ -151,6 +151,16 @@
         </main>
       </div>
     </div>
+    <dialog id="delete-plan-dialog" class="workspace-dialog delete-plan-dialog" aria-labelledby="delete-plan-heading" aria-describedby="delete-plan-description">
+      <h2 id="delete-plan-heading">Delete this plan?</h2>
+      <p id="delete-plan-name"></p>
+      <p id="delete-plan-description">This removes the saved plan and its revision history. Completed roast records and inventory history will be kept. This cannot be undone.</p>
+      <p id="delete-plan-error" role="alert"></p>
+      <div class="delete-plan-actions">
+        <button type="button" class="ghost-btn" id="delete-plan-cancel" autofocus>Cancel</button>
+        <button type="button" class="primary-btn" id="delete-plan-confirm">Delete plan</button>
+      </div>
+    </dialog>
     <script type="module" src="/js/plans.js?v=__ASSET_VERSION__"></script>
   </body>
 </html>