feat: launch 3d architecture documentation portal

docs/user-tutorial/navigate-the-model.md

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+---
+title: "Navigate the Model"
+description: "Move through the POC model and inspect architecture elements."
+---
+
+# Navigate the model
+
+Use pointer or keyboard controls exposed by the POC to orbit, pan, zoom, and select. The interaction contract will be refined with the browser prototype.
+
+## Visible result
+
+The selected element exposes its name and architecture responsibility.

docs/user-tutorial/start-here.md

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+---
+title: "Start Here"
+description: "Open the first architecture model and establish the navigation path."
+slug: /
+---
+
+# Start with the browser POC
+
+The first project deliverable is one architecture model rendered in a navigable 3D scene. Use this path to enter the model, orient the camera, and select an architecture element.
+
+## Outcome
+
+You can identify the model boundary and move between its major elements.
+
+## Next step
+
+Continue to [Navigate the Model](./navigate-the-model.md).