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>

templates/partials/header/topbar.tpl

@@ -45,6 +45,12 @@
 					<!-- IMPORT partials/sidebar/notifications.tpl -->
 				</li>
 
+				{{{ if support.visible }}}
+				<li component="support" class="nav-item support dropdown" title="Support inbox">
+					<!-- IMPORT partials/header/support-drawer.tpl -->
+				</li>
+				{{{ end }}}
+
 				{{{ if canChat }}}
 				<li class="nav-item chats dropdown" title="[[global:header.chats]]">
 					<!-- IMPORT partials/sidebar/chats.tpl -->
@@ -115,6 +121,9 @@
 			<div class="wg-topbar__drawer-actions">
 				<a href="{relative_path}/unread"><i class="fa fa-fw fa-inbox" aria-hidden="true"></i><span>[[unread:title]]</span><span component="unread/count" class="badge rounded-1 bg-primary {{{ if !unreadCount.topic }}}hidden{{{ end }}}">{unreadCount.topic}</span></a>
 				<a href="{relative_path}/notifications"><i class="fa fa-fw fa-bell" aria-hidden="true"></i><span>[[global:header.notifications]]</span><span component="notifications/count" class="badge rounded-1 bg-primary {{{ if !unreadCount.notification }}}hidden{{{ end }}}">{unreadCount.notification}</span></a>
+				{{{ if support.visible }}}
+				<a href="{relative_path}/support"><i class="fa fa-fw fa-life-ring" aria-hidden="true"></i><span>Support inbox</span><span component="support/count" class="badge rounded-1 bg-primary {{{ if !support.unreadCount }}}hidden{{{ end }}}">{support.unreadCount}</span></a>
+				{{{ end }}}
 				{{{ if canChat }}}
 				<a href="{relative_path}/user/{user.userslug}/chats{{{ if user.lastRoomId }}}/{user.lastRoomId}{{{ end }}}"><i class="fa fa-fw fa-comment" aria-hidden="true"></i><span>[[global:header.chats]]</span><span component="chat/count" class="badge rounded-1 bg-primary {{{ if !unreadCount.chat }}}hidden{{{ end }}}">{unreadCount.chat}</span></a>
 				{{{ end }}}