Unify all New Page / New Folder buttons across the app

- Add global window.FlowDeck namespace with createPage() and showCreateFolderModal()
- createPage() creates a Notion-style page via /board/api/pages (same as sidebar bottom-right button)
- showCreateFolderModal() opens a global themed modal (dark/light) instead of browser prompt()
- All New Page buttons now call window.FlowDeck.createPage()
- All New Folder buttons now call window.FlowDeck.showCreateFolderModal()
- Global New Folder modal uses existing .flowdeck-modal CSS classes for theme consistency
- Updated Ctrl+N keyboard shortcut to use unified createPage()

app/templates/library.html

@@ -186,7 +186,7 @@
   <div class="lib-header">
     <h1>Library</h1>
     <div class="lib-header-actions">
-      <button class="lib-btn-primary" @click="newPage()">
+      <button class="lib-btn-primary" onclick="window.FlowDeck.createPage()">
         <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><line x1="12" y1="5" x2="12" y2="19"/><line x1="5" y1="12" x2="19" y2="12"/></svg>
         New page
       </button>
@@ -326,7 +326,7 @@
 
   <!-- "+ Add new" (root level) -->
   <div class="add-new-row" x-show="!loading && tab !== 'favorites' && tab !== 'shared' && tab !== 'published' && tab !== 'repository'"
-       @click="addNewPage(0)">
+       onclick="window.FlowDeck.createPage()">
     <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><line x1="12" y1="5" x2="12" y2="19"/><line x1="5" y1="12" x2="19" y2="12"/></svg>
     Add new
   </div>
@@ -541,7 +541,7 @@ function libraryPage() {
         // ── Synthetic "+ Add new" placeholder row for an expanded parent ──
         if (item._isAddNew) {
           var pad = 30 + (item.depth || 0) * 20;
-          html += '<div class="add-new-under" style="padding-left:' + pad + 'px" onclick="window._libData.addNewPage(' + item._parentId + ')">';
+          html += '<div class="add-new-under" style="padding-left:' + pad + 'px" onclick="window.FlowDeck.createPage()">';
           html += '<svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><line x1="12" y1="5" x2="12" y2="19"/><line x1="5" y1="12" x2="19" y2="12"/></svg> Add new</div>';
           continue;
         }