fix: arborescence dédoublée + dossiers fermés visibles + preview pages FlowDeck

1. Tree affichage: displayTree contient maintenant les racines uniquement
   (plus de flatten). _markTree ajoute depth/db_id sans aplatir, et
   renderChildren gère la récursion. Les enfants n'apparaissent plus
   quand le dossier est fermé, et plus de dédoublement à l'ouverture.

2. Filtre: _filterTree travaille sur l'arbre hiérarchique, clone les
   nodes pour préserver la structure.

3. Preview pages FlowDeck: nouvelle API GET /api/local-workspace/page-content/{id}.
   showPreview détecte content_format='file' → /api/files/, sinon → API page-content.
   Plus de 'file not found' sur les fichiers créés dans FlowDeck.

4. API tree: ajout content_format dans la réponse pour distinguer
   fichiers uploadés vs pages FlowDeck.

app/templates/local_workspace.html

@@ -326,25 +326,25 @@ document.addEventListener('alpine:init', function() {
         }
         var r = await fetch(url);
         var d = await r.json();
-        this.tree = this.addDepths(d.tree || [], 0);
-        this.displayTree = this.tree;
+        // Keep tree hierarchical, only roots in displayTree
+        var roots = d.tree || [];
+        this._markTree(roots, 0);
+        this.tree = roots;
+        this.displayTree = roots;
         this.breadcrumb = d.breadcrumb || [];
         this.loaded = true;
       } catch(e) { console.error('Tree load error:', e); this.loaded = true; }
     },
 
-    addDepths(nodes, depth) {
-      var result = [];
+    _markTree(nodes, depth) {
       for (var i=0; i<nodes.length; i++) {
         var n = nodes[i];
         n.depth = depth;
-        n.db_id = n.id;  // Ensure db_id for consistency with renderChildren
-        result.push(n);
+        n.db_id = n.id;
         if (n.children && n.children.length > 0) {
-          result = result.concat(this.addDepths(n.children, depth+1));
+          this._markTree(n.children, depth + 1);
         }
       }
-      return result;
     },
 
     renderChildren(children, depth) {
@@ -402,19 +402,21 @@ document.addEventListener('alpine:init', function() {
     doFilter() {
       var q = (this.searchQuery || '').toLowerCase().trim();
       if (!q) { this.displayTree = this.tree; return; }
-      var self = this;
-      this.displayTree = this.tree.filter(function(n) {
-        return self._itemMatches(n, q);
-      });
+      this.displayTree = this._filterTree(this.tree, q);
     },
-    _itemMatches(node, query) {
-      if ((node.name || '').toLowerCase().indexOf(query) !== -1) return true;
-      if (node.children && node.children.length > 0) {
-        for (var i = 0; i < node.children.length; i++) {
-          if (this._itemMatches(node.children[i], query)) return true;
+    _filterTree(nodes, query) {
+      var result = [];
+      for (var i=0; i<nodes.length; i++) {
+        var n = nodes[i];
+        var filteredChildren = n.children ? this._filterTree(n.children, query) : [];
+        var selfMatches = (n.name || '').toLowerCase().indexOf(query) !== -1;
+        if (selfMatches || filteredChildren.length > 0) {
+          var clone = Object.assign({}, n);
+          clone.children = filteredChildren;
+          result.push(clone);
         }
       }
-      return false;
+      return result;
     },
 
     // ── Preview on hover ──
@@ -426,20 +428,34 @@ document.addEventListener('alpine:init', function() {
       this.previewVisible = true;
       var self = this;
       var wsId = {{ workspace_id }} || 1;
-      var url = '/api/files/' + wsId + '/' + encodeURIComponent(node.name);
-      // Check if image
+
+      // Image preview
       var imgExts = ['.png','.jpg','.jpeg','.gif','.webp','.svg','.bmp','.ico'];
       var isImg = false;
       for (var i=0; i<imgExts.length; i++) {
         if ((node.name||'').toLowerCase().endsWith(imgExts[i])) { isImg = true; break; }
       }
-      if (isImg) {
-        this.previewContent = '<img src="'+url+'" style="max-width:380px;max-height:180px;display:block;">';
+
+      if (node.content_format === 'file') {
+        // Uploaded file: serve from disk
+        var url = '/api/files/' + wsId + '/' + encodeURIComponent(node.name);
+        if (isImg) {
+          this.previewContent = '<img src="'+url+'" style="max-width:380px;max-height:180px;display:block;">';
+        } else {
+          this.previewContent = 'Loading...';
+          fetch(url)
+            .then(function(r) { return r.text(); })
+            .then(function(t) { self.previewContent = t.substring(0, 500); })
+            .catch(function() { self.previewContent = '(preview not available)'; });
+        }
       } else {
+        // FlowDeck page: fetch content via API
         this.previewContent = 'Loading...';
-        fetch(url)
-          .then(function(r) { return r.text(); })
-          .then(function(t) { self.previewContent = t.substring(0, 500); })
+        fetch('/api/local-workspace/page-content/' + node.id)
+          .then(function(r) { return r.json(); })
+          .then(function(d) {
+            self.previewContent = (d.content || '').substring(0, 500);
+          })
           .catch(function() { self.previewContent = '(preview not available)'; });
       }
     },