feat: add mobile new issue navigation (Closes #971)

frontend/index.html

@@ -873,6 +873,11 @@
       <h3 id="create-issue-heading">Capture work</h3>
       <button id="cancel-new-issue" type="button">Cancel</button>
     </div>
+    <nav class="mobile-create-issue-nav" aria-label="New issue sections">
+      <button type="button" data-create-issue-section="describe">Describe</button>
+      <button type="button" data-create-issue-section="evidence">Evidence</button>
+      <button type="button" data-create-issue-section="file">File</button>
+    </nav>
     <aside class="shared-content-conflict" id="shared-content-conflict" aria-live="assertive" hidden>
       <strong>You already have an unfinished issue draft.</strong>
       <span class="small">Resume it, or replace its title and description with the content shared to Stackchain.</span>
@@ -882,6 +887,7 @@
       </div>
     </aside>
     <form class="create-issue-form" id="create-issue-form">
+      <section class="create-issue-describe" id="create-issue-describe">
       <label for="create-issue-title">Title
         <input id="create-issue-title" type="text" maxlength="255" required autocomplete="off" />
       </label>
@@ -913,7 +919,8 @@
         <button id="save-unfiled-issue" type="button">Save to Drafts</button>
         <button id="file-new-issue" type="button">File now</button>
       </div>
-      <section class="create-issue-attachment" aria-labelledby="create-issue-attachment-label">
+      </section>
+      <section class="create-issue-attachment" id="create-issue-evidence" aria-labelledby="create-issue-attachment-label">
         <strong id="create-issue-attachment-label">Photo evidence <span class="small">Optional · Up to 5 · PNG, JPEG, or WebP · 2 MB each</span></strong>
         <div class="issue-attachment-controls photo-evidence-actions">
           <label class="issue-attachment-trigger" for="take-create-issue-photo">Take photo</label>
@@ -1537,6 +1544,7 @@
 <script src="static/voice-issue-capture.js"></script>
 <script src="static/voice-conversation-capture.js"></script>
 <script src="static/create-issue-sheet.js"></script>
+<script src="static/mobile-create-issue-nav.js"></script>
 <script src="static/create-and-start.js"></script>
 <script src="static/assign-and-start.js"></script>
 <script src="static/filed-claim.js"></script>