Release web scroll follow on input intent - #18

What changed

• Release automatic bottom-follow during upward wheel or trackpad input, before the browser dispatches scroll.
• Apply the same early intent handling to touch scrolling and Page Up, Home, and Arrow Up navigation.
• Cancel pending restoration animation frames when the reader expresses history-navigation intent.
• Strengthen the browser regression so the wheel event occurs before the scroll position changes.

Root cause

The first fix correctly reacted to upward scroll, but browsers can materialize content-visibility rows and invoke ResizeObserver after wheel input and before the scroll event. During that interval, bottom-follow remained enabled and the observer could snap the viewport back to the newest edge.

Validation

• Negative control reproduced the premature snap from scrollTop 760 back to 1000.
• 75/75 web unit tests passed.
• TypeScript and Vite production build passed.
• Complete Playwright harness passed: 12 passed, 8 intentional project-specific skips.
• Independent focused verification passed: 10 scroll tests and the desktop Chromium wheel-before-scroll regression.

This changes desktop/web and responsive web behavior only; native phone application code is untouched.