fix: Moved all doc files under the skill folder

[dmartinol]

Summary

Moved all doc files under the skill folder. Rationale:

• Avoid path traversal vulnerability
• Let lola install the docs according to Add supporting files

Exception to this rule: some pack-level metadata (AI index, source attributions) rather than skill docs are kept under <pack>/docs folders. We can review this decision later in another PR.

Added validation script to:

• Enforce skill-local doc links (docs/...) in CI.
• Catch broken or unsafe doc references early, so skills stay portable and reliable.
• Detect symlink chains.

Note:
Some linked files where actually missed, so now they appear as placeholder files with this frontmatter:

---
title: TODO
status: draft
---

We can fix them in another run (at least now we can easily identify them).

Pack(s) affected

• All

Change type

• Update existing skill / agent
• Docs / README
• CI / tooling

CLAUDE.md compliance

• Document consultation: file is read with the Read tool, then declared to the user

Validation

• make validate passes locally