Add Crystal worktree patterns to .gitignore

Added patterns to ignore Crystal worktree directories:
- /worktrees/
- /worktree-*/

This prevents git from tracking temporary Crystal session directories.

Author: Clément VALENTIN

.gitignore

@@ -71,3 +71,7 @@ caddy_config/
 .env.web
 
 tmp/
+
+# Git worktrees (Crystal)
+/worktrees/
+/worktree-*/