Title scene: add simplified Dragon mesh LOD for TUI performance

[flyingrobots]

Summary

The Stanford Dragon title scene currently uses the full mesh in the TUI ray tracer. That is visually impressive, but the Braille terminal output does not need every source triangle to preserve the silhouette and material read.

Proposal

Add an offline-simplified Dragon mesh or deterministic LOD asset for title-screen rendering. Keep the authored scene identity, material facts, object count, and triangle count reporting explicit so the perf overlay shows which mesh fidelity is active.

Acceptance Criteria

• A simplified Dragon asset is checked in or generated by a deterministic build/asset script.
• The default title scene can select the simplified Dragon for live TUI rendering.
• The profiler records before/after close-camera timings at a geometry where the Dragon fills a large portion of the screen.
• The title-scene facts block reports the active triangle count so reviewers can verify the LOD was selected.
• The full-fidelity mesh remains available for previews or future high-quality exports if useful.

Notes

This should stay separate from the startup drawer slice. It is a renderer/performance follow-up, not a startup UX dependency.

[coderabbitai]

🔗 Related PRs

#97 - Add startup scene performance governor [merged]

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[flyingrobots]

The title screen no longer renders on the startup path. As of 14d17b5 and 910373f on #304, jedit opens on an empty viewer, createInitialModelSnapshot loads no meshes and preloads no scene, and the ray-traced backdrop is reachable only by explicit opt-in (the scene picker, the title number keys, or an injected renderer). Two further fixes on #321 closed paths that were switching it on by accident — arrow keys and pointer movement both ran through activateLegacyTitleBackdrop.

This work is therefore no longer on any path a normal launch touches. It is deferred behind the Easter-egg opt-in, not obsolete.

This one is different from the others, though: its stated motivation is gone. The issue exists for "TUI performance" — the full Stanford Dragon mesh being ray-traced on the startup title. Startup now parses no OBJ meshes at all. That change alone took createInitialModelSnapshot from 151.5 ms to 8.3 ms, and the dragon was part of the 1.75 MB of OBJ text removed from the launch path.

So the performance argument for an LOD mesh no longer holds. If an LOD is still wanted it needs a fresh justification — visual quality in the opt-in scene, or frame budget once someone is actually looking at it — rather than startup cost. Worth rewriting or closing on that basis.