fix(ui): clamp deltaTime to 1ms in pose-renderer FPS calc (#519 Bug 2)

[ruvnet]

Closes #519 Bug 2 (FPS shows Infinity).

Root cause

ui/utils/pose-renderer.js:655 did fps = 1000 / deltaTime without a floor. When two render frames land in the same performance.now() tick (common when an animation frame batches multiple renders), deltaTime === 0 and the EMA averageFps = averageFps * 0.9 + Infinity * 0.1 poisons itself permanently. The HUD then reads Infinity FPS until page reload.

Fix

- const deltaTime = currentTime - this.performanceMetrics.lastFrameTime;
+ const deltaTime = Math.max(currentTime - this.performanceMetrics.lastFrameTime, 1);
  const fps = 1000 / deltaTime;

The 1 ms floor caps displayed FPS at 1000 — far above any real render rate (a 240 Hz monitor renders every ~4 ms), so the cap is never observed in practice. Keeps the EMA finite.

Test plan

• Code inspection: only call site touched; rest of updatePerformanceMetrics unchanged
• (Reviewer, optional) Reproduce in browser by rapid-firing render frames; confirm the old build shows Infinity FPS and the new build doesn't

Related

Issue #519 has three other multi-node bugs documented separately:

• Bug 1 (ghost person count) — addressed by PR feat(sensing-server): adaptive person count — RollingP95 + dedup_factor runtime API #491 (awaiting contributor rebase)
• Bug 3 (skeleton flicker) — partially addressed by merged PR fix(sensing-server): handle WebSocket Lagged + add ping keepalive #484 (WS Lagged + ping keepalive)
• Bug 4 (jumpy vitals) — fixed by merged PR fix(vital_signs): use circular variance for wrapped phases #595 (vital_signs circular variance)

This PR closes only Bug 2 cleanly. The other three are tracked in their own threads.

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