feat: @-mention autocomplete; consultant bounty-board access; clickable atomization tasks

- @-mentions: typing "@" in task comments, the messages composer and the chat
  widget now opens a user picker (new shared mention.js) that inserts "@Name ".
  Backed by the existing /api/v1/users search; menus de-dupe per field.
- Consultants can now open the bounty board (read-only): nav link + page/API
  access extended to consultants, board visibility resolves their assigned
  customers, and cards show "Open" instead of claim actions for non-developers.
- Atomization board task titles (roots and subtasks) link to /tasks/{id} so
  consultants can reach the detail view (comments, assignment, timeline).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/static/js/atomization.js

@@ -82,7 +82,7 @@ function renderRoot(root) {
     ? '<span class="badge" style="color:var(--err)" title="No longer returned by the upstream system">orphaned</span>' : '';
   card.innerHTML = `
     <div class="spread">
-      <h3>${icon} ${esc(root.title)} ${statusBadge(root)} ${orphan}</h3>
+      <h3>${icon} <a href="/tasks/${root.id}">${esc(root.title)}</a> ${statusBadge(root)} ${orphan}</h3>
       <span class="muted">${esc(cust ? cust.name : '')} ${root.external ? '· ' + esc(root.external.key) : ''}</span>
     </div>
     <p class="muted">${esc((root.description || '').slice(0, 240))}</p>
@@ -135,7 +135,7 @@ function renderChildren(parent, kids, depth) {
       <div class="spread">
         <span>
           ${k.status === 'atomized' ? `<input type="checkbox" data-sel aria-label="Select ${esc(k.title)} for publishing" ${selected.has(k.id) ? 'checked' : ''}>` : ''}
-          <strong>${esc(k.title)}</strong> ${ext} ${statusBadge(k)}
+          <a href="/tasks/${k.id}"><strong>${esc(k.title)}</strong></a> ${ext} ${statusBadge(k)}
         </span>
         <span>bounty <strong data-bounty>${k.bounty}</strong></span>
       </div>