fix(markdown): enable config file discovery for markdownlint-cli2

lua/lazyvim/plugins/extras/lang/markdown.lua

@@ -56,11 +56,23 @@ return {
   {
     "mfussenegger/nvim-lint",
     optional = true,
-    opts = {
-      linters_by_ft = {
-        markdown = { "markdownlint-cli2" },
-      },
-    },
+    opts = function(_, opts)
+      opts.linters_by_ft = opts.linters_by_ft or {}
+      opts.linters_by_ft.markdown = { "markdownlint-cli2" }
+
+      opts.linters = opts.linters or {}
+      opts.linters["markdownlint-cli2"] = {
+        -- Disable stdin to enable config file discovery.
+        -- markdownlint-cli2 traverses directories to find .markdownlint.json,
+        -- .markdownlint-cli2.jsonc, etc., but this only works with file paths.
+        stdin = false,
+        args = {},
+        parser = require("lint.parser").from_errorformat("%f:%l:%c %m,%f:%l %m", {
+          source = "markdownlint",
+          severity = vim.diagnostic.severity.WARN,
+        }),
+      }
+    end,
   },
   {
     "neovim/nvim-lspconfig",