Make installed skills self-contained

[tmusser]

What changed

• inlined the critical uncertainty, handoff, and mutation contract into every SKILL.md
• removed repository-relative skill links to ../../references and ../../templates
• added a portability validator that rejects relative links escaping a skill folder
• added installer smoke checks for the portable contract and stale external paths
• made downstream skills explicitly accept fact ledgers and conversation-state records
• clarified the README quickstart and portable install behavior

Why

Every skill linked to ../../references/shared-output-contract.md, but the installer only copies skill folders. Three skills also linked to ../../templates/CONVERSATION_STATE.md, while optional templates are installed to a different namespaced location.

The source repository validated, but installed skills silently lost the common safety contract and contained broken supporting links. That undermined the central product promise: moving from context to action without laundering uncertainty.

Impact

Installed Claude and Codex skill folders are now self-contained. Critical rules travel inside each SKILL.md, including this invariant:

Do not promote an assumption, inference, open question, proposed action, or stakeholder position into a fact, decision, commitment, owner, or deadline without new source support.

No skill names, schemas, install destinations, or mutation permissions changed.

Validation

All checks passed on the final head:

• Python compilation
• installer dry-run, reinstall, force-replace, and unknown-skill smoke tests
• installed-skill portability checks
• Claude user, Codex user, and Codex project install checks
• repository structure validation
• example validation
• schema validation
• diff formatting