fix(treesitter): pin to archived master branch

The config uses the legacy `nvim-treesitter.configs` API, which the
`main` rewrite dropped. Without an explicit branch pin, `Lazy sync`
jumped to `main` and broke startup (module 'nvim-treesitter.configs'
not found). Pin both treesitter and treesitter-textobjects to `master`
and refresh the lockfile to a known-good synced state.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lua/plugins/treesitter.lua

@@ -1,9 +1,12 @@
 return {
   {
     "nvim-treesitter/nvim-treesitter",
+    -- Pin to archived `master` branch: this config uses the legacy
+    -- `nvim-treesitter.configs` API, which the `main` rewrite dropped.
+    branch = "master",
     dependencies = {
       "JoosepAlviste/nvim-ts-context-commentstring",
-      "nvim-treesitter/nvim-treesitter-textobjects",
+      { "nvim-treesitter/nvim-treesitter-textobjects", branch = "master" },
     },
     config = function(_, opts)
       require("nvim-treesitter.configs").setup(opts)