Topbar unread drawer (#28)

Adds an Unread dropdown to the topbar utilities (before notifications), per docs/superpowers/plans/2026-07-17-topbar-unread-drawer.md.

- New partial `templates/partials/header/unread-drawer.tpl`: toggle with live `component="unread/count"` badge (core socket updates), server-rendered empty/footer rows.
- `public/client.js`: on dropdown open, fetches `GET /api/unread` and injects up to 10 topic rows (titles/categories via textContent only); fetch failure falls back to the empty state.
- Mobile burger drawer gets an Unread row with the same badge.
- SCSS: unread dropdown joins the shared dropdown width rule; flex row styles for topic items.

Deviations from the plan's example code, found by live verification against the dev forum:
- Plan's `api.get('/unread')` hits the v3 write API and 404s → replaced with a fetch of the `/api/unread` read route.
- NodeBB 4 has no global `window.require`, so runtime translation of the static `[[unread:...]]` strings never ran → those strings are now server-rendered in the template (also removes the plan's translate-over-innerHTML step, which would have re-parsed untrusted titles as HTML).

Verified: full plain-node test suite passes; Playwright against the dev container passed all checks (badge count, item ordering before notifications, dropdown topic links + navigation, /unread footer link, mobile drawer badge at 390px).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #28
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
Co-committed-by: vickydotbat <vickydotbat@tutamail.com>

templates/partials/header/unread-drawer.tpl

@@ -0,0 +1,9 @@
+<a class="nav-link dropdown-toggle d-flex gap-2 align-items-center" href="#" role="button" data-bs-toggle="dropdown" aria-haspopup="true" aria-expanded="false" aria-label="[[unread:title]]">
+	<i class="fa fa-fw fa-inbox" aria-hidden="true"></i>
+	<span component="unread/count" class="badge rounded-1 bg-primary {{{ if !unreadCount.topic }}}hidden{{{ end }}}">{unreadCount.topic}</span>
+</a>
+<ul class="dropdown-menu wg-topbar__dropdown unread-dropdown p-1 shadow" role="menu" data-wg-unread-menu>
+	<li data-wg-unread-loading class="dropdown-item disabled"><i class="fa fa-fw fa-spinner fa-spin" aria-hidden="true"></i> [[unread:title]]</li>
+	<li data-wg-unread-empty class="hidden"><span class="dropdown-item disabled">[[unread:no-unread-topics]]</span></li>
+	<li data-wg-unread-footer><hr class="dropdown-divider"><a class="dropdown-item wg-unread-item--all" href="{relative_path}/unread">[[unread:title]]</a></li>
+</ul>