fix: keep plugin artifact hooks self-contained

[Q00]

Summary

• make repo Claude hooks work when CLAUDE_PLUGIN_ROOT is unset by falling back to the checkout cwd
• include the declared skills directory inside the .claude-plugin artifact so plugin.json skills path resolves for artifact installs

Original PR blocker coverage

Addresses plugin artifact / local hook blockers reported on #1136 and #1187. Version drift was rechecked with scripts/sync-plugin-version.py --check and is currently clean on main.

Verification

• python3 -m json.tool .claude/settings.json >/dev/null
• test -f .claude-plugin/skills/setup/SKILL.md
• test -f .claude-plugin/skills/auto/SKILL.md

[shaun0927]

Cross-checked against #961 (which classifies #1205–#1217 as adjacent post-merge fixes, not new substrate) and against the two referenced blockers #1136 / #1187. The two behavioral changes are narrow:

1. Repo-checkout fallback for CLAUDE_PLUGIN_ROOT so dev-mode hooks resolve when the var is unset.
2. Bundling the declared skills directory inside .claude-plugin/ so artifact installs can resolve skills/auto/SKILL.md (and siblings).

The rest of the +4930 LoC is the bundled SKILL.md copies themselves, which is mechanical and matches the upstream skills/ sources. No conflicts with #1194 / #1196 / #1205 / #1213 since this PR doesn’t touch src/ouroboros/auto/* or mcp/tools/auto_handler.py. Safe to land any time after #1195/#1196/#1194 — order doesn't matter for merge.