feat(panel): polish v002.1 readiness presentation

[hkimw]

Refs #125, #126.

Summary

• Render the existing KV260 readiness surface in a no-script VS Code webview when available, with output-channel text retained as fallback.
• Add the aperture-mark header, PASS/PENDING/FAIL status pills, and collapsible evidence-path details for each checklist item.
• Add maintainer-style empty-state copy for missing launcher status input and unreachable board snapshots.

Tests

• node --check editors/vscode-prototype/src/kv260-status-panel.mjs
• node --check editors/vscode-prototype/src/extension.mjs
• node --check editors/vscode-prototype/test/kv260-status-panel.test.mjs
• node --check editors/vscode-prototype/test/extension-entrypoint.test.mjs
• node editors/vscode-prototype/test/kv260-status-panel.test.mjs
• node editors/vscode-prototype/test/extension-entrypoint.test.mjs
• node editors/vscode-prototype/test/static-boundary.test.mjs
• node editors/vscode-prototype/test/extension-manifest.test.mjs
• python3 -m pytest tests/test_kv260_status.py