refactor: scenes now folder-based with preview image support

static/js/pages/scene.js

@@ -215,8 +215,10 @@ const PageScene = {
 
     _sceneCardHtml(scene) {
         const canvasCount = (scene.canvases || []).length;
+        const preview = scene.preview_ext ? `/scene/${scene.id}/preview.${scene.preview_ext}` : '';
         return `<div class="glass-card scene-card" data-scene-id="${scene.id}" data-action="render">
-            <div class="scene-card-name">${scene.name}</div>
+            ${preview ? `<div style="height:120px;background:url(${preview}) center/cover;border-radius:8px 8px 0 0"></div>` : ''}
+            <div class="scene-card-name" style="${preview?'':'padding-top:18px'}">${scene.name}</div>
             <div class="scene-card-game" style="margin-bottom:6px">${this._currentGameName || '未关联游戏'}</div>
             <div class="scene-card-meta"><span>${canvasCount} 画布</span><span>${scene.updated_at ? new Date(scene.updated_at).toLocaleDateString() : ''}</span></div>
             <div class="scene-canvas-list">${(scene.canvases||[]).map(c => `<span class="scene-canvas-badge">${c.label||c.width+'x'+c.height}</span>`).join('')}</div>