feat: add mobile checklist steps inline (Closes #915)

frontend/index.html

@@ -605,6 +605,16 @@
     <button class="issue-retry" id="retry-issue-load" type="button" hidden>Reload latest issue</button>
     <div class="row"><span id="issue-labels"></span><span class="small" id="issue-assignees"></span></div>
     <div class="issue-sheet-content markdown-content" id="issue-sheet-body"></div>
+    <section class="checklist-add" aria-label="Add checklist step">
+      <button id="open-add-checklist-step" type="button" disabled>Add step</button>
+      <form id="add-checklist-step-form" hidden>
+        <label class="visually-hidden" for="add-checklist-step">Checklist step</label>
+        <input id="add-checklist-step" type="text" maxlength="240" autocomplete="off" placeholder="New checklist step" />
+        <button id="save-checklist-step" type="submit">Add</button>
+        <button id="cancel-checklist-step" type="button">Cancel</button>
+      </form>
+      <div id="add-checklist-step-status" class="small" aria-live="assertive"></div>
+    </section>
     <section class="checklist-completion" id="checklist-completion" aria-label="Completed checklist" hidden>
       <span id="checklist-completion-status" role="status" aria-live="polite">Checklist complete</span>
       <button id="complete-checklist-issue" type="button">Close issue</button>