Lint Markdown prose with Vale

Extend the ClearProse em dash ban from reStructuredText to Markdown, so
the rule covers all our prose rather than only Sphinx documentation.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: adamtheturtle

.pre-commit-config.yaml

@@ -289,7 +289,7 @@ repos:
         stages: [pre-commit]
 
       # Vale enforces prose style rules, such as banning em dashes, in
-      # reStructuredText files.
+      # reStructuredText and Markdown files.
       # The rules come from the ``ClearProse`` package pinned in ``.vale.ini``,
       # which ``vale sync`` downloads into the (gitignored) ``styles``
       # directory.
@@ -303,7 +303,7 @@ repos:
         entry: uv run --extra=dev vale sync
         language: python
         pass_filenames: false
-        files: (\.rst$|^\.vale\.ini$)
+        files: (\.(rst|md)$|^\.vale\.ini$)
         additional_dependencies:
           - *uv_version
         stages: [pre-commit]
@@ -312,7 +312,7 @@ repos:
         name: vale
         entry: uv run --extra=dev vale
         language: python
-        types_or: [rst]
+        types_or: [rst, markdown]
         require_serial: true
         additional_dependencies:
           - *uv_version

.vale.ini

@@ -3,5 +3,5 @@ MinAlertLevel = error
 
 Packages = https://github.com/adamtheturtle/vale-style-clear-prose/releases/download/v1.1.0/ClearProse.zip
 
-[*.rst]
+[*.{rst,md}]
 BasedOnStyles = ClearProse