Add skill stewardship review workflow

[kargarisaac]

Summary

• add the skill stewardship registration, refresh, proposal, diff, and apply/reject workflow across CLI/API/dashboard
• add scoped candidate record loading, auto-apply policy controls, artifact-surface validation, and atomic apply safety
• polish the Skills dashboard review UI with line-numbered diffs/full-file previews and opaque confirmation dialogs

Review notes

• subagent review found release blockers around artifact path scope, concurrent apply rollback, and untracked server modules
• fixed path validation to only allow scanned artifact files plus new skill reference/example files
• fixed apply to re-check proposal status under a SQLite immediate write lock before writing files

Validation

• uv run pytest: 1850 passed, 118 skipped
• uv run pytest tests/unit/context/test_store_search.py tests/unit/skill_stewardship/test_repository_and_pipeline.py tests/unit/skill_stewardship/test_artifacts.py: 86 passed
• uv run ruff check
• uv run vulture src/lerim/ vulture_whitelist.py
• uv run --extra docs mkdocs build --strict
• npm run build
• git diff --check