feat: recursive tree, drag & drop, sub-folders in sidebar workspace

- _load_workspace_pages now recursively loads children via _load_children()
- Sidebar: recursive Jinja2 macro render_workspace_tree()
- Drag & drop: HTML5 DnD — drag files into folders or reorder
- move API: PUT /api/local-workspace/items/{id}/move
- Folder hover shows 📄 (new file) + 📁 (sub-folder) buttons
- newPageInFolder/newFolderInFolder with parent_id for nesting
- Visual: dragging opacity + drop target highlight
- Items indented by depth (16px per level)

app/routers/board.py

@@ -141,7 +141,7 @@ def _build_page_tree(conn, parent_id: int | None, ws_key: str, depth: int = 0, m
 
 
 def _load_workspace_pages(ws_cookie: str) -> list:
-    """Load top-level pages for the active workspace."""
+    """Load top-level pages with children for the active workspace."""
     if not ws_cookie:
         return []
     try:
@@ -151,12 +151,39 @@ def _load_workspace_pages(ws_cookie: str) -> list:
                 "SELECT id, title, parent_section FROM pages WHERE workspace_id=? AND parent_id IS NULL ORDER BY created_at DESC",
                 (ws_id,),
             ).fetchall()
-        return [{"db_id": r["id"], "name": r["title"] or "Untitled", "id": f"page/{r['id']}",
-                 "icon": "📁" if r["parent_section"] == "Workspace" else "📄"} for r in rows]
+        items = []
+        for r in rows:
+            items.append({
+                "db_id": r["id"], "name": r["title"] or "Untitled", 
+                "id": f"page/{r['id']}",
+                "icon": "📁" if r["parent_section"] == "Workspace" else "📄",
+                "is_folder": r["parent_section"] == "Workspace",
+                "children": _load_children(r["id"]),
+            })
+        return items
     except (ValueError, Exception):
         return []
 
 
+def _load_children(parent_id: int) -> list:
+    """Recursively load children of a page."""
+    with get_conn() as conn:
+        rows = conn.execute(
+            "SELECT id, title, parent_section FROM pages WHERE parent_id=? ORDER BY created_at",
+            (parent_id,),
+        ).fetchall()
+    children = []
+    for r in rows:
+        children.append({
+            "db_id": r["id"], "name": r["title"] or "Untitled",
+            "id": f"page/{r['id']}",
+            "icon": "📁" if r["parent_section"] == "Workspace" else "📄",
+            "is_folder": r["parent_section"] == "Workspace",
+            "children": _load_children(r["id"]),
+        })
+    return children
+
+
 def _sidebar_data(request: Request, owner: str = "", repo: str = "") -> dict:
     user = SessionManager.decode_session(request.cookies.get("flowdeck_session", ""))
     ws_name = user.get("login", "Bruno") if user else "Bruno"