test: symlinked .mintlify/skills directory

[skeptrunedev]

Summary

• Moves skill files to a top-level skills/ directory
• Symlinks .mintlify/skills -> ../skills to test symlink support for skill discovery

Test plan

• Verify deployment picks up skills through the symlink
• Check /.well-known/skills/index.json lists both skills

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Note

Low Risk
Low-risk documentation/config change, but relies on deployment tooling correctly resolving the new .mintlify/skills symlink.

Overview
Adds a .mintlify/skills entry that points to ../skills to support serving skills from a top-level skills/ directory via symlink.

Updates the skill.md docs (ai/skillmd.mdx) with a new section explaining how to symlink .mintlify/skills (or individual skills) to avoid duplicating files, noting that symlinks are resolved during deployment.

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