fix(viewer): clamp GLB floor animation on slow frames

[FenjuFu]

What does this PR do?

Fixes #616 by clamping the remaining GLB floor-animation interpolation factor to 1. A slow frame or resumed background tab can otherwise move baked floors past their target and make their positions diverge. This matches the already-clamped parametric LevelSystem; walkthrough mode still snaps to the baked elevation.

How to test

1. Load a multi-floor baked GLB and switch between stacked and exploded modes.
2. Exercise slow frames or resume a suspended tab; floors should stay between their previous and target elevations.
3. Enter walkthrough mode and confirm floors immediately use their baked elevations.

Focused validation executed the actual priority-5 useFrame callback extracted from the source with the TypeScript AST, using structural level objects. All 14 stacked/exploded cases passed for frame deltas of 0, 1/60, 1/12, 0.1, 0.2, 0.5, and 30 seconds; ordinary-frame behavior and walkthrough snapping were preserved. At 0.5-second frames, the original callback diverged to approximately -4.5e28 while the fix settled at the expected 7.7 m elevation. This is deterministic frame-callback validation, not a full browser render.

Pinned Biome 2.4.16 and git diff --check passed. Complete fork CI also passed: lint/format, agent-skill validation, type checking, the full test suite, application/package builds, and the macOS packed CLI/runtime smoke test. The validation branch contains the same fix plus isolated CI-trigger configuration; those workflow changes are not part of this PR.

Screenshots / screen recording

No UI layout change; the regression concerns slow-frame level transforms.

Checklist

• I've tested this locally with bun dev
• My code follows the existing code style (file-scoped pinned Biome passed)
• I've updated relevant documentation (not applicable)
• This PR targets the main branch

[pascal]

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