feat: attach screenshots to update replies (Closes #527)

frontend/index.html

@@ -516,6 +516,15 @@
       <textarea id="update-reply" maxlength="10000" placeholder="Write a reply"></textarea>
       <div class="mention-options" id="update-reply-mentions" role="listbox" aria-label="Teammates" hidden></div>
       <div class="mention-status small" id="update-reply-mention-status" aria-live="polite"></div>
+      <div class="issue-attachment-controls">
+        <input class="visually-hidden" id="update-reply-attachment" type="file" accept="image/png,image/jpeg,image/webp" />
+        <label class="issue-attachment-trigger" for="update-reply-attachment">Attach screenshot</label>
+      </div>
+      <div class="issue-attachment-preview" id="update-reply-attachment-preview" hidden>
+        <img id="update-reply-attachment-image" alt="Selected screenshot preview" />
+        <span class="small" id="update-reply-attachment-meta"></span>
+        <button id="remove-update-reply-attachment" type="button">Remove screenshot</button>
+      </div>
       <div class="update-reply-actions">
         <button id="send-update-reply" type="button">Send reply</button>
         <button id="send-update-reply-read-next" type="button">Reply, mark read &amp; next</button>