Remove releases from git tracking and clean up MD5 checksums

- Remove all release packages from git tracking (kept locally)
- Delete MD5 checksum files, keeping only SHA256
- Update .gitignore to exclude releases/ directory
- Update CLAUDE.md release documentation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -32,4 +32,8 @@ notes.*
 
 # local code
 wordpress
-core
+core
+wp-core
+
+# Releases (not tracked in git)
+/releases/