Exclude Reddit URLs from link checker

Reddit returns 403 Forbidden for automated link checkers even with custom user agents,
causing false positives in the dead link detection. These links work fine for regular users.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: ironicbadger

.github/workflows/check-links.yml

@@ -39,6 +39,8 @@ jobs:
             --exclude "example.org"
             --exclude "plausible.ktz.cloud"
             --exclude "techhub.social"
+            --exclude "reddit.com"
+            --exclude "www.reddit.com"
             --exclude-path node_modules/
             --exclude-path .git/
             '**/*.md'