feat: markdown opt-in extra + fix local.lua load order

.gitignore

@@ -9,6 +9,10 @@ spell/
 # nvim-pack-lock.json in version control - see :help vim.pack-lockfile
 # For the official `nvim-lua/kickstart.nvim` git repository, we leave it ignored to avoid unneeded
 # merge conflicts.
-nvim-pack-lock.json
+# nvim-pack-lock.json
 
 .DS_Store
+
+# Per-machine local overrides — each machine maintains its own copy, never committed.
+# See lua/local.lua.example for available options.
+lua/local.lua