feat: support additional agent harnesses

[Raithlin]

Summary

• Add Cursor, Hermes Agent, and OpenClaw global skill installation and auto-detection.
• Track skill ownership, refuse to overwrite unowned skills, and preserve user edits during updates and uninstall.
• Report modified skills in agent inventory and update harness documentation.
• Gate gha update on the skill's declared command requirements against the running binary's available capabilities; preserve files and report missing capabilities when incompatible.
• Add package-manager distribution to the roadmap.

Verification

• GOCACHE=/tmp/gha-go-build GOMODCACHE=/tmp/gha-go-mod make check (lint, race tests, and 95% coverage gate)
• Temporary-home CLI smoke run for install, list, dry-run, and safe uninstall.
• Rebuilt bin/gha and checked its JSON capability inventory.