Add Gate demo ecosystem bridge

[SemeAIPletinnya]

Cross-agent recovery

Recovered the one-file Gate demo bridge left by the interrupted Axiom premium task. No Gate logic, API behavior, receipt contract, or deployment configuration is changed.

Objective

Connect the existing gate.semeai.tech demo surface back to the public SemeAI product ecosystem without turning the API surface into decorative UI.

What changed

• Adds a compact ecosystem navigation bar to demo/saas_visible.html.
• Links the product, Gate contract, Genesis, API, and live Gate demo surfaces.
• Preserves the existing demo application and all SaC/PoR/Gate behavior.

Governance preserved

• SaC semantics: unchanged.
• PoR semantics: unchanged.
• Gate semantics: unchanged.
• Post-Gate mutation: none.
• Legacy receipt_id: unchanged.
• External LLM/private retrieval/retention: none.

Validation

• python -m pytest — 104 passed.
• git diff --check — PASS.
• The frontend counterpart passed its full regression and rendered admission matrix.

Deployment and rollback

After required checks and review pass, merge to master and use only the repository's existing GitHub Pages/deployment mechanism for the demo surface. No DNS, API, or infrastructure mutation is part of this PR. Rollback is a normal revert/redeploy of this isolated HTML change.