feat: launch 3d architecture documentation portal

architecture/overview.md

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+---
+title: "Architecture Overview"
+description: "Understand the browser POC responsibilities and boundaries."
+slug: /
+---
+
+# Shape the browser POC
+
+The POC separates model data, scene composition, interaction, and presentation so each concern can change as the product learns.
+
+The first architecture decision is to keep the model representation independent from the 3D renderer.

architecture/poc-shape.md

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+---
+title: "POC Shape"
+description: "Trace one model from source data to an interactive 3D scene."
+---
+
+# Trace the rendering path
+
+1. A local model fixture describes architecture elements and relationships.
+2. A scene adapter maps records to spatial objects.
+3. The renderer presents the scene in a browser.
+4. Interaction state connects selection to readable details.
+
+This shape supports a focused experiment without committing to a production authoring format.