Don't load tree-sitter-manager.nvim when tree-sitter-cli is missing

lua/plugins/treesitter.lua

@@ -1,6 +1,18 @@
+local has_tree_sitter_cli = vim.fn.executable('tree-sitter') == 1
+
+if not has_tree_sitter_cli then
+  vim.schedule(function()
+    vim.notify(
+      'tree-sitter-cli not found on PATH; tree-sitter-manager.nvim disabled',
+      vim.log.levels.WARN
+    )
+  end)
+end
+
 return {
   {
     'romus204/tree-sitter-manager.nvim',
+    cond = has_tree_sitter_cli,
     lazy = false,
     config = function()
       require('tree-sitter-manager').setup({