fix(web): stop resting canvas chart loops

[xingkaixin]

Summary

• add a shared demand-driven canvas frame loop with active, idle, and stopped states
• suspend chart work outside the viewport or while the page is hidden
• stop settled bar, donut, and tile charts while preserving data, hover, resize, and theme wakeups
• cache resolved palettes and keep tile pointer work local to each chart host

Performance

• settled charts now keep zero animation frames pending instead of recursively scheduling forever
• hover drift and glow decay run at 20 fps; morph and growth remain full-rate while active
• computed styles are resolved once per chart input or theme change rather than once per frame

Test plan

• pnpm lint
• pnpm format:check
• pnpm test
• pnpm build

Issue: CS-191