feat(buzz-persona): define portable Agent Skill content

[wolfyy970]

Summary

A Skill selected for an agent should still be the same Skill when that agent runs somewhere else, not whichever same-named folder happens to exist on the new machine.

This gives buzz-persona one runtime-neutral representation for a complete Agent Skills directory:

• exact bytes, including scripts, empty files, binary assets, and executable intent
• spec-valid metadata and stable content digests
• portable path validation and an exact review inventory
• allowed-tools shown as an untrusted request, never a permission

It also exposes a validated SKILL.md parser and per-Skill validation, digest, and inspection APIs that #5301 can use without treating a name or local path as portable identity.

Scope

No archive, persistence, installation, activation, or permission grant. Those belong in later layers.

Testing

• just ci
• adversarial tests for path handling, Unicode, identity, size limits, metadata, and binary content

Related

• feat(agent): per-agent skill allowlist + Skill selection UI #5301
• Agent Snapshot v2: reviewable Skills and tool requirements #5267

[wolfyy970]

I have restacked this onto current main. It now owns only exact portable Skill content and shared parsing; installation and activation remain separate.

[chatgpt-codex-connector]

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[wolfyy970]

@wpfleger96, this gives #4485 a shared, exact Skill content model without adding installation or activation authority. Could you review that boundary when you have a moment?

[wolfyy970]

Closing this. Skills should land on the shared definition shapes once those exist, not as a separate stack.