perf: render loop, ML pipeline, and effects optimizations

[Ghostkwebb]

Summary

Performance optimizations across the render loop, ML pipeline, and effects system.

Changes

• Fix clock.getDelta() bug — called twice per frame; second call returned ~0, breaking effect timing
• Batch rain particles — single stroke() call instead of per-particle (3-5x faster)
• Zero-copy ML frame transfer — OffscreenCanvas + ImageBitmap replaces getImageData() readback
• Cache DOM refs — eliminates 60 getElementById calls/sec in effect loop
• for...in loops — replaces Object.keys().forEach in hot paths
• Fix redundant bone lookups — getNormalizedBoneNode() called twice for same key
• Visibility toggle — replaces ppScene.add/remove per frame
• Debounce config saves — 500ms debounce prevents IPC spam
• Date.now() — replaces new Date().getTime()
• Guard updateLog() — skips work when log panel is hidden
• Sync version to 2.6.1

[Wei-1]

Awesome! LGTM!