[Feature]: Remove outdated TODO comment in useScrollSync and align docs with implementation

[yejiming]

Feature Description

The useScrollSync hook currently contains a TODO saying we should consider replacing setTimeout with requestAnimationFrame, but the implementation already uses requestAnimationFrame as the primary path and only falls back to setTimeout.

Problem Statement

This outdated TODO creates confusion for maintainers and reviewers, because comments no longer reflect the actual behavior. It also increases cognitive load when debugging scroll-sync behavior.

Proposed Solution

• Remove or rewrite the outdated TODO comment in src/renderer/pages/conversation/Preview/hooks/useScrollSync.ts.
• Keep a concise note explaining the current strategy:
  • prefer requestAnimationFrame
  • fallback to setTimeout for compatibility/safe degradation
• Ensure Chinese/English comments remain semantically consistent.

Feature Category

UI/UX Improvement

Additional Context

Relevant lines:

• Outdated TODO comment: lines 62–63
• Existing requestAnimationFrame implementation: lines 87–92
• Fallback setTimeout: lines 95–98

[cdxiaodong]

Handled in the PR that updates useScrollSync comments to match the current implementation.

What changed:

• remove the outdated TODO about replacing setTimeout
• explain that the hook already prefers requestAnimationFrame
• document setTimeout as the compatibility fallback in both Chinese and English comments

Validation:

• bun run lint
• bun run format
• bunx tsc --noEmit
• bun run test