Add Design Genome for divergent frontend art direction

[Sparvovic]

What changed

• add frontend-divergence, a reusable skill that generates and selects structurally distinct, brief-fit web art directions before implementation
• add a deterministic standard-library direction engine with cross-project fingerprint history and privacy-preserving project hashes
• add tests enforcing deterministic output, brief fit, generic-default limits, and at least five differing design axes between concepts
• document installation and make the package validator cover every skill rather than only bootstrap-project

Why

Quality-oriented frontend skills often converge on the same safe composition. Design Genome inserts productive friction before coding: morphological exploration, explicit concept selection, a frozen design contract, and a final anti-template challenge.

User impact

Codex can implicitly trigger the skill for greenfield websites and significant redesigns, while exact design reproduction and small UI maintenance remain out of scope. The selected contract is then handed to existing frontend or taste skills for implementation quality.

Validation

• python skills/frontend-divergence/scripts/test_direction_lab.py
• python scripts/validate.py
• system quick_validate.py skills/frontend-divergence
• git diff --check
• local/public separation guard

All checks passed. No automatic merge is requested.