fix: Library preserves sidebar tree and categorizes by parent_section

- Sidebar data (board._sidebar_data()) no longer overwritten by library content
- New variables: lib_recent, lib_favorites, lib_shared, lib_private
- Pages categorized by parent_section column: Private/Favorites/Shared
- Recents tab shows all non-trashed pages ordered by updated_at
- library.html updated to use lib_* variables instead of sidebar data
- Favorites/Shared tabs hidden when empty (lib_has_favorites/lib_has_shared)

app/templates/library.html

@@ -15,12 +15,16 @@
   <button class="view-tab" :class="{ active: tab === 'recents' }" @click="tab = 'recents'">
     <span class="tab-icon">🕒</span> Recents
   </button>
+  {% if lib_has_favorites %}
   <button class="view-tab" :class="{ active: tab === 'favorites' }" @click="tab = 'favorites'">
     <span class="tab-icon">⭐</span> Favorites
   </button>
+  {% endif %}
+  {% if lib_has_shared %}
   <button class="view-tab" :class="{ active: tab === 'shared' }" @click="tab = 'shared'">
     <span class="tab-icon">👥</span> Shared
   </button>
+  {% endif %}
   <button class="view-tab" :class="{ active: tab === 'private' }" @click="tab = 'private'">
     <span class="tab-icon">🔒</span> Private
   </button>
@@ -61,8 +65,8 @@
 
   <!-- Recents -->
   <div x-show="tab === 'recents'">
-    {% for page in recent_pages %}{{ page_row(page) }}{% endfor %}
-    {% if not recent_pages %}
+    {% for page in lib_recent %}{{ page_row(page) }}{% endfor %}
+    {% if not lib_recent %}
     <div class="lib-empty">
       <div style="font-size:48px;margin-bottom:16px;">🕒</div>
       <h3>No recent pages</h3>
@@ -72,8 +76,8 @@
 
   <!-- Favorites -->
   <div x-show="tab === 'favorites'">
-    {% for page in favorite_pages %}{{ page_row(page) }}{% endfor %}
-    {% if not favorite_pages %}
+    {% for page in lib_favorites %}{{ page_row(page) }}{% endfor %}
+    {% if not lib_favorites %}
     <div class="lib-empty">
       <div style="font-size:48px;margin-bottom:16px;">⭐</div>
       <h3>No favorites</h3>
@@ -84,17 +88,20 @@
 
   <!-- Shared -->
   <div x-show="tab === 'shared'">
+    {% for page in lib_shared %}{{ page_row(page) }}{% endfor %}
+    {% if not lib_shared %}
     <div class="lib-empty">
       <div style="font-size:48px;margin-bottom:16px;">👥</div>
       <h3>No shared pages</h3>
       <p>Shared pages from your team will appear here.</p>
     </div>
+    {% endif %}
   </div>
 
   <!-- Private -->
   <div x-show="tab === 'private'">
-    {% for page in private_pages %}{{ page_row(page) }}{% endfor %}
-    {% if not private_pages %}
+    {% for page in lib_private %}{{ page_row(page) }}{% endfor %}
+    {% if not lib_private %}
     <div class="lib-empty">
       <div style="font-size:48px;margin-bottom:16px;">🔒</div>
       <h3>No private pages</h3>