Restore world-space ambient occlusion radius

[andeplane]

Summary

Ambient occlusion looked absent on the diffusion example. The earlier SSAO noise fix (#435) put N8AO in screen-pixel radius mode, where Atomify's radius of 10 spans less than one atom and the pass degrades to a faint edge detector. N8AO's AO-only debug view was almost pure white.

• Keep the occlusion radius in simulation units, so buried atoms stay dark however far the camera is. Verified against the example thumbnail look.
• Keep the detailed sampling (64 AO / 16 denoise): magnified crops show the grain from Fix ugly lines in SSAO #65 is a sample-count problem, present only at the fast mode, not a radius problem.
• Ignore a persisted ssaoRadius/ssaoIntensity from the removed legacy slider, so a stale saved value cannot silently change the look now that the radius is honoured in world units.
• The SSAO e2e spec now perturbs the radius mode before each settings change so it proves the reset instead of N8AO's default, and drops the unread screenshots.

Validation

• npm run typecheck, 485 unit tests, e2e/ssao-quality.spec.ts pass.
• Headless quick run of the diffusion example through the real code path: AO-only view shows clear depth structure; before it was near white.

Follow-ups (out of scope)

• omovi renders the AO-off path without the sRGB output transform, so toggling AO also shifts brightness. That is an omovi bug.
• The 10-unit radius suits LJ and Å-scale examples; deriving it from the model size would make it robust for unusual scales.
• The fast quality mode still shows the Fix ugly lines in SSAO #65 grain at this radius. It is the explicit lower-cost choice in Settings.

🤖 Generated with Claude Code

https://claude.ai/code/session_01NMqBT1iPcu3ayt1QdXuWB1