Support symlinks in .claude/commands/ (same as .claude/rules/)

Summary

.claude/rules/ follows symlinks for file discovery, but .claude/commands/ does not. Symlinked .md files in the commands directory are silently ignored during skill registration.

Reproduction

1. create a command file at .claude/commands/utils/my-command.md
2. symlink it: ln -s utils/my-command.md .claude/commands/my-command.md
3. only utils:my-command registers as a skill; /my-command does not appear

Use case

I share a single .claude/ directory (via symlink) across multiple repos and machines. Commands live in subdirectories for organisation, with top-level symlinks for convenient access. This pattern works everywhere except command discovery.

Expected behavior

Symlinked .md files in .claude/commands/ should be resolved and registered as skills, consistent with .claude/rules/ behavior.