Add alias symlinks for shorter skill references

[erdemtuna]

Problem

With the upcoming host/owner/repo/skillName install layout, referencing installed skills from other skills becomes verbose:

Follow the guidance in `github.com/lossyrob/phased-agent-workflow/skill-creator`.

Proposal

During craft install, create alias-based symlinks alongside the canonical paths:

<target>/
├── github.com/lossyrob/phased-agent-workflow/paw-implement/  ← canonical
├── github.com/anthropics/skills/skill-creator/                ← canonical
├── paw -> github.com/lossyrob/phased-agent-workflow/          ← symlink
└── anthropic -> github.com/anthropics/skills/                 ← symlink

This lets skill authors write shorter references in SKILL.md:

Follow the guidance in `paw/skill-creator`.

The symlink resolves on disk — no mapping file needed, AI agents can read the skill directly.

Notes

• Only applies to direct dependencies (they have user-chosen aliases)
• Symlinks should be cleaned up on craft remove
• craft install should recreate symlinks if alias changes
• Depends on: namespaced install layout (host/owner/repo) being implemented first