Add open-pr skill and link from CLAUDE.md

[VPDPersonal]

Summary

• Adds .claude/skills/open-pr/SKILL.md — a project skill that captures Aspid.FastTools PR conventions: title format, .github/PULL_REQUEST_TEMPLATE.md body shape (Summary / Notes for review / Linked issues), label policy, commit-message rules (no Co-Authored-By: Claude … trailers), scope hygiene, and a recipe checklist.
• Replaces the long ad-hoc section I first wrote in CLAUDE.md with a 5-line Pull request conventions pointer that quotes the must-know rules and points at the skill for the full procedure.
• Registers the new skill in the Local Claude Code automation list next to build-generator and sync-readmes.

Notes for review

Triggered by #16, where @claude opened a PR titled Claude/add onenable idregistry i bk jl with an empty body — exactly the failure mode this skill is meant to prevent. Skill-form has two advantages over a passive CLAUDE.md section:

• The agent can be explicitly directed at the procedure (open-pr).
• The procedure can be detailed (recipe, common failure modes, gh-cli HEREDOC pitfall) without bloating CLAUDE.md.

The CLAUDE.md pointer is kept because Claude Code Action reads CLAUDE.md as passive context — without it the skill might never get invoked. The pointer summarises the five rules that must apply even if the skill is missed.

Documentation-only — no code, no runtime impact.

Linked issues

(none)