feat(review): generate repo-specific Claude Code / Codex skill files

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Context

Part of the repo-specific CLAUDE.md/AGENT.md generation roadmap. Some repos have a contribution or review workflow complex enough that a single CLAUDE.md/AGENT.md cannot reasonably cover it -- this repo's own one-shot-gate contribution flow is the clearest example, which is why it carries a dedicated skill file rather than folding the whole procedure into AGENT.md. This issue extends the generation engine to also propose scoped skill files (for example a contributing-to-this-repo skill, or a repo-specific review/testing skill) when the extracted repo profile indicates that kind of complexity.

Goal

Extend generation to conditionally produce scoped skill files alongside CLAUDE.md/AGENT.md when the repo profile signals a non-trivial workflow.

Requirements

• Reuse the repo-profile-extraction primitive and the PR-delivery path from the earlier issues in this roadmap; do not build a parallel delivery mechanism.
• Define an explicit trigger condition on the repo profile (e.g. presence of a one-shot or auto-merge/auto-close gate, multi-stage CI, non-obvious linked-issue rules) that decides whether a skill file is proposed at all -- do not generate a skill file for every repo unconditionally.
• Generated skill files follow the same structural convention as this repo's own skills under .claude/skills (frontmatter description plus procedural body).
• Skill file proposals are additive to the same pull request as the CLAUDE.md/AGENT.md changes, or a clearly linked follow-up PR -- not a separate silent write.

Deliverables

• Trigger-condition logic that decides when a skill file is warranted, backed by test cases for both the trigger and no-trigger paths
• Skill-file content generator producing frontmatter plus procedural body in this repo's existing skill format
• Delivery wired into the same PR-opening path used for CLAUDE.md/AGENT.md

Expected outcomes

• A repo with a complex, non-obvious contribution gate receives a proposed skill file describing that flow, without requiring a maintainer to hand-write it
• A repo with a simple, conventional contribution flow does not receive a skill-file proposal

Part of the repo-doc generation roadmap: #2993

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JSO-2560