feat: add asset-first Artic show preview bundle

[baskduf]

Summary

• Rework @artic show from a single static HTML preview into a provenance-recorded asset-first preview bundle under .artic/show/.
• Add separated styles.css, tokens.json, report.json, critique.md, selected.json, iteration directories, and assets/manifest.json provenance tracking.
• Add 3D/runtime-aware preview placeholders, scoring/reporting, strict threshold handling, stale iteration cleanup, and payload aliases for host verification.
• Sync canonical skill docs, Claude/Codex plugin mirrors, and localized README contract text.

Findings closed

• Fixed unrecorded root-level 3D/runtime assets by recording root aliases in assets/manifest.json.
• Fixed stale iterations/002 and iterations/003 remaining after rerunning @artic show --max-iterations 1.
• Fixed README/localized README drift from the old “safe static preview” contract.

Verification

• git diff --check origin/main...HEAD
• static added-line scan: 0 debug markers, 0 secret-like additions, 0 dangerous Python additions, 0 conflict markers
• python3 -m py_compile skills/artic/scripts/*.py tests/*.py scripts/*.py
• python3 -m pytest -q → 107 passed
• targeted show/readme tests → passed
• 3D/stale/provenance smoke → passed; no unrecorded assets, stale iterations cleared, modified_app_files == []
• fresh sdist/wheel/skill archive build + scripts/check_release_artifacts.py → passed
• independent final re-review → PASS; no blocking or non-blocking findings

Notes

• @artic show still does not modify app/source files.
• External asset downloading remains future scope; this PR implements generated placeholders and catalog-reference provenance for preview bundles.