Add design and product documentation

PRODUCT.md

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+# Product — Lineform Studio
+
+Status: approved baseline.
+
+## Audience and job
+
+Prospective architecture clients and collaborators need to assess built work, understand the studio process, and submit a qualified project brief.
+
+## Primary journeys
+
+1. Explore projects through typology, place, scale, and completion evidence.
+2. Understand services, process, and studio point of view.
+3. Submit a brief with location, scope, timing, and constraints.
+
+## Non-goals
+
+- No generic stock architecture, invented awards, or lead forms without project context.
+
+## Success criteria
+
+Work remains the dominant proof, project metadata is scannable, and the brief form is the clear conversion path.