feat(browser-actions): visible pointer, human-paced motion and smooth scroll step

[chubes4]

Fixes #2547.

• presentation-json=<object|@file> turns on an opt-in presentation layer. It's off by default, and existing runs are unchanged.
  • pointer: a cursor element in an isolated shadow root with pointer-events: none, re-injected on navigation, following real mouse positions
  • clickFeedback: a ripple at the click point
  • motion: an eased pointer move to the target before click/hover/fill/type/select
  • typing: per-character delay for type, and for fill when applyToFill is set
• New scroll step: selector | position: "top"|"bottom" | by: {x,y}, plus behavior and block. It waits until scrolling settles. (The issue's to was renamed to position to avoid colliding with drag.to.)
• New module browser-presentation.ts. The validator covers the new step and options. README is documented.

Tests

npm run build clean. New browser-actions-presentation-validation.test.ts 2/2 and browser-actions-presentation.browser.test.ts 1/1: the pointer survives navigation, doesn't intercept clicks, and a scroll reaches its target. test:browser-video-capture 3/3. browser-preview-routing 16/16.

Drafted by a Homeboy cook (cook-detached-52c9b48c). Its gates passed, but finalization refused because the candidate changed after promotion. With Chris's authorization, it was rebased onto current main as a single commit, re-verified, and published outside Homeboy.

AI-assisted: drafted by an OpenCode agent, reviewed and finalized by Extra Chill Bot.