Sync mattpocock agent skills to latest upstream

[kmcginnes]

Description

Re-syncs the vendored mattpocock/skills agent skills into .agents/skills/ (mirrored via symlinks into .claude/ and .kiro/), bringing them to their latest upstream versions. No product code, dependencies, or user-facing behavior changes.

Core change — the skill set shifts:

• Added: code-review, implement, research, to-spec, to-tickets, wayfinder
• Removed: to-issues, to-prd (superseded by to-tickets/to-spec)
• Updated: content refreshed across ask-matt, codebase-design, domain-modeling, grilling, handoff, prototype, tdd (dropped refactoring.md), triage, writing-great-skills, and others

Supporting — skills-lock.json updated to match: new entries added, to-issues/to-prd pruned so the manifest matches disk.

Validation

• skills-lock.json is valid JSON and every entry maps to a skill dir on disk (no drift in either direction)
• Mirror parity verified: every .agents/skills/* skill has live (non-dangling) symlinks in both .claude/skills/ and .kiro/skills/
• No dangling cross-links to the removed tdd/refactoring.md
• No product code touched, so pnpm checks / pnpm test surface is unaffected

Related Issues

• None