feat(v5.10.0): v5.4.0 + v5.5.0 features — backlinks, page/collection duplication, trash purge, version history, markdown import, embed/bookmark/video/audio blocks, cover & icon, OG metadata

- Migration v7: page_versions table + pages.cover_url/page_icon columns
- Trash service (purge_expired 30-day) + daily scheduler
- Board API: duplicate page, backlinks, versions (snapshot/list/restore), cover/icon upload, markdown/file import
- Collections API: duplicate collection (deep copy properties/views/pages/data sources)
- Export service: render embed/bookmark/video/audio in markdown/HTML/PDF/public
- Public page renderer: cover image + icon
- Editor: slash commands for media blocks, lightbox, version history UI, backlinks panel, cover/icon picker, import modal
- OG metadata endpoint for bookmark cards
- 386 tests passing

app/templates/public_page.html

@@ -137,7 +137,16 @@
 </header>
 
 <main class="pub-container">
-  <h1 class="pub-title">{{ title }}</h1>
+  {% if cover_url %}
+  <div class="pub-cover" style="position:relative;margin:-40px -24px 32px;height:240px;overflow:hidden;">
+    <img src="{{ cover_url }}" style="position:absolute;inset:0;width:100%;height:100%;object-fit:cover;">
+    <div style="position:absolute;inset:0;background:linear-gradient(180deg,rgba(0,0,0,0) 50%,rgba(0,0,0,.5) 100%);"></div>
+  </div>
+  {% endif %}
+  <div style="display:flex;align-items:center;gap:12px;margin-bottom:8px;">
+    <span class="pub-icon" style="font-size:2rem;">{{ page_icon or fd_icon('file',24) }}</span>
+    <h1 class="pub-title">{{ title }}</h1>
+  </div>
   {% if updated_at %}
   <div class="pub-meta">Last updated: {{ updated_at[:10] }}</div>
   {% endif %}