feat: implement new grid creation with inline rename in DataGridsManager

- Add new_grid() method to create empty DataGrid under selected folder/leaf parent
  - Generate unique sheet names (Sheet1, Sheet2, ...) with _generate_unique_sheet_name()
  - Auto-select and open new node in edit mode for immediate renaming
  - Fix TreeView to cancel edit mode when selecting any node
  - Wire "New grid" icon to new_grid() instead of clear_tree()
  - Add 14 unit tests covering new_grid() scenarios and TreeView behavior

src/myfasthtml/controls/DataGridsManager.py

@@ -50,7 +50,7 @@ class Commands(BaseCommands):
     return Command("NewGrid",
                    "New grid",
                    self._owner,
-                   self._owner.new_grid)
+                   self._owner.new_grid).htmx(target=f"#{self._owner._tree.get_id()}")
   
   def open_from_excel(self, tab_id, file_upload):
     return Command("OpenFromExcel",
@@ -104,6 +104,62 @@ class DataGridsManager(SingleInstance, DatagridMetadataProvider):
     file_upload.set_on_ok(self.commands.open_from_excel(tab_id, file_upload))
     return self._tabs_manager.show_tab(tab_id)
   
+  def new_grid(self):
+    selected_id = self._tree.get_selected_id()
+
+    if selected_id is None:
+      parent_id = self._tree.ensure_path("Untitled")
+    else:
+      node = self._tree._state.items[selected_id]
+      if node.type == "folder":
+        parent_id = selected_id
+      else:  # leaf
+        parent_id = node.parent
+
+    namespace = self._tree._state.items[parent_id].label
+    name = self._generate_unique_sheet_name(parent_id)
+
+    dg_conf = DatagridConf(namespace=namespace, name=name)
+    dg = DataGrid(self, conf=dg_conf, save_state=True)
+    dg.init_from_dataframe(pd.DataFrame())
+    self._registry.put(namespace, name, dg.get_id())
+
+    tab_id = self._tabs_manager.create_tab(name, dg)
+    document = DocumentDefinition(
+      document_id=str(uuid.uuid4()),
+      namespace=namespace,
+      name=name,
+      type="excel",
+      tab_id=tab_id,
+      datagrid_id=dg.get_id()
+    )
+    self._state.elements = self._state.elements + [document]
+
+    tree_node = TreeNode(
+      id=document.document_id,
+      label=name,
+      type="excel",
+      parent=parent_id,
+      bag=document.document_id
+    )
+    self._tree.add_node(tree_node, parent_id=parent_id)
+
+    if parent_id not in self._tree._state.opened:
+      self._tree._state.opened.append(parent_id)
+
+    self._tree._state.selected = document.document_id
+    self._tree._start_rename(document.document_id)
+
+    return self._tree, self._tabs_manager.show_tab(tab_id)
+
+  def _generate_unique_sheet_name(self, parent_id: str) -> str:
+    children = self._tree._state.items[parent_id].children
+    existing_labels = {self._tree._state.items[c].label for c in children}
+    n = 1
+    while f"Sheet{n}" in existing_labels:
+      n += 1
+    return f"Sheet{n}"
+
   def open_from_excel(self, tab_id, file_upload: FileUpload):
     excel_content = file_upload.get_content()
     df = pd.read_excel(BytesIO(excel_content), file_upload.get_sheet_name())
@@ -257,7 +313,7 @@ class DataGridsManager(SingleInstance, DatagridMetadataProvider):
   def mk_main_icons(self):
     return Div(
       mk.icon(folder_open20_regular, tooltip="Upload from source", command=self.commands.upload_from_source()),
-      mk.icon(table_add20_regular, tooltip="New grid", command=self.commands.clear_tree()),
+      mk.icon(table_add20_regular, tooltip="New grid", command=self.commands.new_grid()),
       cls="flex"
     )
   

src/myfasthtml/controls/TreeView.py

@@ -184,10 +184,10 @@ class TreeView(MultipleInstance):
     self._state = TreeViewState(self)
     self.conf = conf or TreeViewConf()
     self.commands = Commands(self)
-
+    
     if items:
       self._state.items = items
-
+    
     if self.conf.icons:
       self._state.icon_config = self.conf.icons
   
@@ -350,6 +350,7 @@ class TreeView(MultipleInstance):
   
   def _save_rename(self, node_id: str, node_label: str):
     """Save renamed node with new label."""
+    logger.debug(f"_save_rename {node_id=}, {node_label=}")
     if node_id not in self._state.items:
       raise ValueError(f"Node {node_id} does not exist")
     
@@ -393,7 +394,9 @@ class TreeView(MultipleInstance):
     """Select a node."""
     if node_id not in self._state.items:
       raise ValueError(f"Node {node_id} does not exist")
-    
+
+    # Cancel edit mode when selecting
+    self._state.editing = None
     self._state.selected = node_id
     return self
   
@@ -401,11 +404,11 @@ class TreeView(MultipleInstance):
     """Render action buttons for a node (visible on hover)."""
     is_leaf = len(self._state.items[node_id].children) == 0
     conf = self.conf
-
-    add_visible    = conf.add_leaf    if is_leaf else conf.add_node
-    edit_visible   = conf.edit_leaf   if is_leaf else conf.edit_node
+    
+    add_visible = conf.add_leaf if is_leaf else conf.add_node
+    edit_visible = conf.edit_leaf if is_leaf else conf.edit_node
     delete_visible = conf.delete_leaf if is_leaf else conf.delete_node
-
+    
     buttons = []
     if add_visible:
       buttons.append(mk.icon(add_circle20_regular, command=self.commands.add_child(node_id)))
@@ -413,7 +416,7 @@ class TreeView(MultipleInstance):
       buttons.append(mk.icon(edit20_regular, command=self.commands.start_rename(node_id)))
     if delete_visible:
       buttons.append(mk.icon(delete20_regular, command=self.commands.delete_node(node_id)))
-
+    
     return Div(*buttons, cls="mf-treenode-actions")
   
   def _render_node(self, node_id: str, level: int = 0):