fix(treesitter): disable matchup treesitter integration for markdown

Markdown injection parsing (bash/sh code blocks) triggers a nil-node
crash in vim-matchup on InsertEnter. Disable matchup's treesitter engine
for markdown to fall back to the working regex-based matching.

Author: Venkata Subramani Renduchintala

lua/plugins/configs/treesitter.lua

@@ -117,6 +117,9 @@ return {
 				-- enables vim-matchup integration
 				enable = true,
 				enable_quotes = true,
+				-- markdown injections (bash/sh code blocks) trigger a nil-node crash
+				-- in the treesitter injection layer; fall back to regex matching there
+				disable = { "markdown" },
 			},
 			-- incremental_selection = {
 			--     enable = true,