feat(links): check internal /blog/ links resolve to a post (#199)

* feat(links): pre-commit check that /blog/<slug>/ links resolve to a post in _posts/

Git-Session-Id: 1e32

* fix(links): drop or repair 28 internal blog links to missing posts

Git-Session-Id: 1e32

* fix(precommit): skip deleted files in internal blog link check

Pre-commit passes staged paths including deletions; read_text() on a
deleted post crashed the hook with FileNotFoundError. Skip nonexistent
paths and cover it with a regression test.

Git-Session-Id: dcc56cb0-de33-5447-b1f6-ae482c644aeb

Author: TimeToBuildBob

.pre-commit-config.yaml

@@ -64,6 +64,16 @@ repos:
         files: '(_posts/.*\.md|scripts/generate_og_images\.py|_config\.yml)'
         stages: [pre-commit]
 
+  # Internal blog links must resolve to a post in _posts/ (unpublished posts 404)
+  - repo: local
+    hooks:
+      - id: check-internal-blog-links
+        name: Check Internal Blog Links
+        entry: python3 scripts/precommit/check_internal_blog_links.py
+        language: system
+        files: '^_posts/.*\.md$'
+        stages: [pre-commit]
+
   # Markdown link checks
   - repo: local
     hooks: