feat: manage issue blockers in app (Closes #531)

frontend/index.html

@@ -307,6 +307,16 @@
       <h2 id="issue-blockers-title">Blocked by</h2>
       <div class="issue-blocker-list" id="issue-blocker-list"></div>
       <div id="issue-blocker-status" class="small" aria-live="polite"></div>
+      <button id="manage-issue-blockers" type="button" hidden>Add blocker</button>
+      <button id="start-unblocked-issue" type="button" hidden>Start now</button>
+      <div class="issue-blocker-manager" id="issue-blocker-manager" hidden>
+        <label for="issue-blocker-search">Search open issues</label>
+        <input id="issue-blocker-search" type="search" maxlength="100" autocomplete="off"
+          role="combobox" aria-controls="issue-blocker-results" aria-expanded="false" />
+        <div id="issue-blocker-results" role="listbox" aria-label="Open issue results"></div>
+        <div id="issue-blocker-search-status" class="small" aria-live="polite"></div>
+        <button id="cancel-issue-blocker" type="button">Cancel</button>
+      </div>
     </section>
     <h2>Full conversation</h2>
     <div id="issue-comments"></div>