Port templates to NodeBB 4.14 benchpress escaping

NodeBB 4.14 registers a real __escape for template rendering (4.13 used
identity), so raw-HTML output must use the double-brace forms:
- HTML helpers: {{buildAvatar(...)}}, {{buildCategoryIcon(...)}}, etc.
- Pre-rendered HTML fields: {{txEscape(content)}} / {{./descriptionParsed}}
- Token-bearing text (nav labels, category names): {{tx(...)}}
- emails/partials/post-queue-body.tpl also adopts the 4.14 data shape
  (notification.category/topic/user/content).

Mirrors the harmony 2.2.72 -> 3.0.15 and core 4.13.2 -> 4.14.0 diffs.

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

templates/emails/notification.tpl

@@ -20,7 +20,7 @@
 <tr class="notification-body">
 <td style="padding: 20px 40px; font-family: Jost, system-ui, -apple-system, 'Segoe UI', Roboto, Arial, sans-serif; font-size: 15px; line-height: 20px; color: #3a3340;">
 <p style="margin: 0; padding: 6px 0px; font-family: Jost, system-ui, -apple-system, 'Segoe UI', Roboto, Arial, sans-serif; font-size: 13px; line-height: 26px; color: #3a3340;">
-{body}
+{{txEscape(body)}}
 </p>
 </td>
 </tr>