feat: rebuild landing page with product evidence

[bymilon]

Outcome

Replaces the rejected template-like marketing page with an Impeccable-led, evidence-first landing surface for the five-team design-partner pilot.

What changed

• establishes PRODUCT.md and DESIGN.md with explicit brand, truthfulness, and anti-slop rules
• replaces cream/moss/terracotta editorial styling with a restrained white/cobalt instrument system
• leads with a clearly labelled sample OpenAPI contract-review artifact
• separates proposed workflow, current evidence, explicit non-capabilities, and the founding offer
• adds founder-led response expectations and warns against emailing confidential contracts
• preserves the qualified mailto, hypothesis, bounded conversion events, and no-JavaScript behavior
• records desktop, mobile, and 200%-equivalent visual evidence

Validation

• bun run check
• 12 unit/security tests
• 3 Playwright journeys including axe, keyboard, JavaScript-disabled, and narrow-screen checks
• Impeccable detector: 0 findings
• independent visual review: no P0 blocker; every original P0/P1 design defect resolved

Gates

Preview acceptance, merge, outreach resumption, and production/custom-domain deployment remain separately gated.