Cluster demo: Precision/Voltage concepts with screen-space reflections

[corepunch]

What

Rebuilds apps/cluster-demo to match two concept frames (01 Classic / Precision, 03 Cool / Voltage) and makes screen-space reflections work in the engine.

Scene (apps/cluster-demo/blender/build_cluster.py → tools/blender-export.py)

• Classic: black-chrome mirror cups that reflect the neon ring and needle, spun dial faces, a recessed centre screen with a mirror road floor, glass plaques for the speed and the temperature/clock, and a glossy chin that mirrors the glows.
• Voltage: neon chevron blade corridor (value-driven fill across the stack, depth falloff), glass gauge cards, mirror deck with an animated dot matrix, bottom info bar.
• New shader groups, each a Blender node graph plus matching GLSL: IC_Neon, IC_DialFace, IC_Glass, IC_Plaque, IC_DotGrid, IC_Road, IC_Mirror (SSR + studio cubemap). The studio softboxes are one table in studio.py, used by both the cubemap bake and the Blender preview.
• Oil gauge removed: neither concept has one. Demo curves and the navigation test were updated to match.

Engine

• Two-pass SSR (plugins/SceneKit/RenderPass.c, source/renderer/r_main.c): reflective models draw their base in the main pass, the frame is captured, then they draw again adding only the reflected light (additive, no depth write). Glows drawn over reflective surfaces survive and show up in reflections. The shader tells the passes apart by u_sceneTextureSize (0 in the main pass).
• Blended materials no longer write depth unless the shader sets DepthWriteEnabled. Depth state no longer carries over between draws, which was hiding dial numerals.
• Supporting pieces: cubemap sampler uniforms, the scene capture API (ScreenSpaceCapture, Model3D.ScreenSpaceReflectionEnabled), and tests: test_shader_uniforms.c, test_screen_space_capture.c (now links and renders into its own depth FBO, since the macOS offscreen surface has no depth), test_scene_reflections.lua.

Tooling / app

• Exporter draw order: opaque siblings now come before blended ones (back to front by bounding-box centre).
• Exporter package.lua check: missing property types are matched by whole name (Fade was treated as present because FadeIn existed).
• Cluster controller: RenderScreen never reached Lua and Screen is not a Node (no KeyDown). The controller now initialises from an orca.async coroutine and handles keys as Viewport_KeyDown with focus on the Viewport. CLUSTER_DEMO_START=voltage starts on Voltage for captures.

Testing

• make test-headless passes.
• make test-screen-space-capture passes.
• build/bin/orca -test=apps/cluster-demo/Tests/navigation.lua passes.
• Ran the exported app. It loads with no shader or resource errors, and SSR reflections show on the chrome, chin and decks (design/*-orca.jpg).

Reviewer notes

• Arrow keys untested by hand: real Left/Right presses haven't been tried, because synthetic keystrokes don't reach the bare binary.
• Engine captures predate the last tuning: design/*-orca.jpg were taken before the final blade/falloff tweak (the display locked). design/*-blender.png show the current state.
• Generated content: Meshes/, Materials/, Shaders/, Scenes/ and Animations.* are exporter output.
• History: apps/cluster-demo/HANDOVER.md has the full background.

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