docs: add interactive SkipHow presentation explainer - #81

Summary

• add a standalone Russian-language interactive explainer for the SkipHow responsibility contract and package shape
• keep the presentation self-contained with no remote runtime or data requests
• use an AA-compliant text accent while preserving the original decorative vermilion

Verification

• I added or updated tests when behavior changed, or verified the standalone artifact directly.
• I ran python scripts/check.py and the relevant focused checks.
• I ran git diff --check.
• Packaging is unchanged, so host installation checks are not required for this PR.

Desktop and 390px mobile renders were inspected. The network trace contained only the local HTML request, console output was clean, and all panels remained interactive.

Notes

Adds docs/presentation/README.md and docs/presentation/skiphow-explainer.html. Claims follow the existing README, evidence, decisions, and design records.