feat: domain-model-coverage skill -- compute coverage of artefacts against domain model

[AlexMikhalev]

Summary

Create a Claude Code skill that computes coverage of project artefacts against the active domain model.

Context

Two coverage scripts exist:

• scripts/domain-model/validate-knowledge-base.py -- KB term coverage
• publishing/scripts/compute-coverage.py -- per-chapter manuscript coverage

This skill generalises coverage to:

• Client projects: PVVH, FBB, risk register against domain model terms
• Product projects: user stories, feature specs against domain model
• Knowledge base: research notes against active project terms

Acceptance Criteria

• Computes per-document coverage ratio
• Reports missing terms and fuzzy near-misses (via terraphim-agent suggest)
• Supports configurable thresholds per project type
• JSON output for CI/CD integration
• Exit code 1 if overall coverage below threshold

Dependencies

• terraphim-ai #546 (coverage --schema CLI) -- optional, Python fallback works
• terraphim-skills Epic: Publishing domain model skills for terraphim v1.9 dynamic ontologies #43 (publishing skills epic)