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/gitea_workspace.html

@@ -779,7 +779,7 @@ document.addEventListener('alpine:init', () => {
     <div class="gw-content">
       <div style="display:flex;align-items:center;justify-content:space-between;margin-bottom:16px;">
         <h3>🔒 Private Pages</h3>
-        <button class="btn btn-primary" @click="newPrivate()">+ New Page</button>
+        <button class="btn btn-primary" onclick="window.FlowDeck.createPage()">+ New Page</button>
       </div>
       <template x-if="privatePages.length === 0">
         <div class="empty-state" style="padding:40px 20px;">