Add design and product documentation

DESIGN.md

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+# Design — Northyard Residences
+
+## Direction
+
+Premium residential editorial with light stone tones, precise plans, quiet bento composition, and photography-led confidence.
+
+## System
+
+- Reuse semantic tokens and reserve accent color for availability and action.
+- Balance generous editorial space with dense apartment facts.
+- Plans must remain legible and never become decorative thumbnails.
+- Motion supports spatial orientation and gallery continuity; reduced-motion fallback is required.
+- Mobile keeps price, availability, plan, and enquiry action together.

PRODUCT.md

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+# Product — Northyard Residences
+
+Status: approved baseline.
+
+## Audience and job
+
+Home buyers and advisers need to understand the development, compare available apartments, inspect plans and amenities, estimate financing, and request a qualified consultation.
+
+## Primary journeys
+
+1. Understand location, architecture, amenities, and delivery status.
+2. Filter apartments and inspect plan, area, floor, orientation, price, and availability.
+3. Explore financing and submit a contextual enquiry.
+
+## Non-goals
+
+- No fabricated availability, guaranteed investment returns, or hidden price conditions.
+
+## Success criteria
+
+Apartment comparison is clear, factual claims are sourced, and the enquiry preserves the selected property context.