feat(markdown-config): register markdown as an org src-block language

`#+begin_src markdown ... #+end_src' blocks rendered and exported
fine but `org-lint' warned on every one of them ("Unknown source
block language: 'markdown'"), and `C-c '' inside the block fell
back to `fundamental-mode' instead of opening it in
`markdown-mode' for editing.

Add a `with-eval-after-load 'org' form that pushes
`("markdown" . markdown)' onto `org-src-lang-modes'.  New ERT test
in `tests/test-markdown-config.el' asserts the entry resolves to
`markdown' after `(require 'markdown-config)'.

Surfaced while clearing `org-lint' on `todo.org' from 55 issues
down to 1 -- the last one was this warning on a Linear ticket-body
draft that was genuinely markdown.  Registering the language is
the right fix; relabeling the block as `text' or `example' would
lose accuracy.

1 files changed, 27 insertions, 0 deletions

diff --git a/tests/test-markdown-config.el b/tests/test-markdown-config.el
new file mode 100644
index 00000000..62d199a8
--- /dev/null
+++ b/tests/test-markdown-config.el
@@ -0,0 +1,27 @@
+;;; test-markdown-config.el --- Tests for markdown-config -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Covers the org-side wiring in markdown-config.el.  The use-package
+;; block for markdown-mode itself is upstream config; the assertion
+;; here is on the local glue that points org at markdown-mode for
+;; `#+begin_src markdown' blocks.
+
+;;; Code:
+
+(require 'ert)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+
+;; Require org BEFORE markdown-config so the `with-eval-after-load
+;; 'org' body fires synchronously instead of being deferred.
+(require 'org)
+(require 'markdown-config)
+
+(ert-deftest test-markdown-config-registers-markdown-org-src-lang ()
+  "Normal: `markdown' shows up in `org-src-lang-modes' mapped to
+`markdown' so org-lint stops warning on `#+begin_src markdown' and
+`C-c '' opens those blocks in `markdown-mode'."
+  (should (equal (cdr (assoc "markdown" org-src-lang-modes)) 'markdown)))
+
+(provide 'test-markdown-config)
+;;; test-markdown-config.el ends here