feat: guard mobile Draft capacity (Closes #623)

frontend/index.html

@@ -593,6 +593,20 @@
   </section>
 </div>
 
+<div class="draft-capacity-sheet" id="draft-capacity-sheet" role="dialog" aria-modal="true" aria-labelledby="draft-capacity-heading" hidden>
+  <section class="draft-capacity-panel">
+    <h3 id="draft-capacity-heading">Drafts full — nothing was deleted.</h3>
+    <p class="small">Review saved work, keep editing, or explicitly replace the oldest Draft.</p>
+    <div class="draft-capacity-oldest" id="draft-capacity-oldest"></div>
+    <div class="draft-capacity-actions">
+      <button id="review-full-drafts" type="button">Review Drafts</button>
+      <button id="keep-editing-draft" type="button">Keep editing</button>
+      <button id="replace-oldest-draft" type="button">Replace oldest &amp; save</button>
+    </div>
+    <div id="draft-capacity-status" class="small" aria-live="assertive"></div>
+  </section>
+</div>
+
 <div class="update-sheet" id="update-sheet" role="dialog" aria-modal="true" aria-labelledby="update-sheet-title">
   <section class="update-sheet-panel">
     <div class="update-sheet-header">
@@ -844,6 +858,7 @@
 <script src="static/widgets.js"></script>
 <script src="static/drafts.js"></script>
 <script src="static/unfiled-captures.js"></script>
+<script src="static/draft-capacity-dialog.js"></script>
 <script src="static/outbox-coordinator.js"></script>
 <script src="static/background-issue-sync.js"></script>
 <script src="static/issue-outbox.js"></script>