Add a support inbox icon to the topbar (sow-nodebb-plugin-support#10)

Mirrors the existing unread-drawer pattern: a new dropdown next to the
notification bell, gated on templateData.support.visible (injected by
the support plugin's filter:middleware.renderHeader hook, on every page
render, for viewers with any support access at all). Opening it fetches
GET /plugins/support/notifications via the api module, renders up to
10 entries by textContent (never innerHTML), and marks everything read
via POST .../notifications/read, clearing the badge client-side.

Also present in the mobile burger drawer, same gating.

ponytail: no live socket push for this badge (core's own unread/notification
counts get one); it only catches up on the next full page load after the
box is opened. Noted in client.js as the upgrade path if that gap matters.

Verified live against sow-nodebb-plugin-support's dev NodeBB stack (theme +
plugin both mounted): icon hidden for a user with no support access, badge
count and dropdown contents correct for a reviewer, badge clears on open.
Full plain-node test suite passes.

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

scss/westgate/_topbar.scss

@@ -173,7 +173,8 @@ $wg-topbar-panel-bg: rgba(21, 17, 26, 0.98);
 .wg-topbar .notifications-dropdown,
 .wg-topbar .chats-dropdown,
 .wg-topbar .drafts-dropdown,
-.wg-topbar .unread-dropdown {
+.wg-topbar .unread-dropdown,
+.wg-topbar .support-dropdown {
   width: min(24rem, calc(100vw - 1.5rem));
 }
 
@@ -189,6 +190,10 @@ $wg-topbar-panel-bg: rgba(21, 17, 26, 0.98);
   opacity: 0.7;
 }
 
+.wg-topbar .wg-support-item--unread {
+  font-weight: 600;
+}
+
 .wg-topbar .dropdown-item,
 .wg-topbar .btn.btn-ghost,
 .wg-topbar .btn.btn-light {