Add design and product documentation

DESIGN.md

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+# Design
+
+Status: draft required before major visual implementation.
+
+## Required decisions
+
+- Visual direction and anti-directions.
+- Typography, color, spacing, radius, imagery, and icon language.
+- Layout rhythm and responsive priorities.
+- Motion policy, reduced-motion fallback, and performance budget.
+- Accessibility requirements and intentional detector exceptions.
+
+Use semantic Tailwind tokens and existing shadcn primitives. The AI must propose a coherent direction, show the diff, and receive explicit approval before treating it as authoritative.

PRODUCT.md

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+# Product
+
+Status: draft required before major implementation.
+
+## Required decisions
+
+- Audience and primary job-to-be-done.
+- Three most important user journeys.
+- Required pages, content, data, and integrations.
+- Explicit non-goals and legal or operational constraints.
+- Measurable acceptance criteria.
+
+The AI must draft this document from supplied specs and conversation, show the diff, and receive explicit approval before treating it as authoritative.