Reduced motion fix 2

[ameerf-wix]

Description

Reduced motion: detect and enforce prefers-reduced-motion by default

Interact.forceReducedMotion was a plain boolean = false that nothing ever set from the OS preference — and even when set to true,
it was bypassed for any effect whose CSS had been pre-generated, which is the setup the docs recommend. So on a machine with
"reduce motion" on, every animation played at full strength, and five documentation sites said otherwise.

Runtime

• Interact.reducedMotion (new, read-only) — resolves forceReducedMotion ?? matchMedia('(prefers-reduced-motion: reduce)').matches.
  Single source of truth; all seven add.ts call sites read it. false under SSR/JSDOM.
• Interact.forceReducedMotion is now boolean | undefined, default undefined — an override, not the mechanism. true forces reduced
  motion on, false forces motion on.
• Enforcement moved into generated CSS. generate() emits @media (prefers-reduced-motion: reduce) rules alongside the base ones, so
  it holds with JS disabled, under SSR, and across a mid-session preference change with no JS at all.
• Per effect kind: time effects (including iterations: Infinity) collapse to a 1ms single iteration; state effects keep the state
  and drop the tween; viewProgress and pointerMove are cancelled. Nothing is suppressed by name, so a collapsed entrance still
  completes its data-interact-enter handshake and can never be stranded behind its own FOUC hiding rule.
• Per-effect collapse via the effect's own animation custom property — an author's gentler alternative is exempt without touching
  its neighbours on the same target.
• An author-declared prefers-reduced-motion condition wins, at either interaction or effect level. This is how a gentler
  alternative is expressed.
• Scrubs are cancelled unconditionally, in CSS and JS alike, so a scrub's alternative must use a time-based trigger.
• Mid-session reactivity — scrub interactions rebind on a preference change; CSS-backed time and state effects follow it live.
• Fixed: a viewEnter entrance's FOUC hiding rule is now gated on the union of its interaction's and its effect's conditions.
  Previously conditions: ['desktop'] on an entrance left the element permanently hidden on mobile. Pre-existing, not
  reduced-motion-specific.
• Fixed: the two state-effect CSS paths agreed — generate() moved to the runtime's no-preference shape, so runtime output is
  byte-identical to master.

Validation

• REDUCE_GATED_SCRUB (new category REDUCED_MOTION, severity warning) — a viewProgress/pointerMove interaction or effect gated on
  (prefers-reduced-motion: reduce) can never run. A no-preference gate is not reported: redundant, not dead.

Docs

• Canonical ## Reduced motion sections in rules/full-lean.md and docs/guides/conditions-and-media-queries.md; new sections in
  rules/viewprogress.md and rules/pointermove.md; ## Static Properties in docs/api/interact-class.md.
• Corrected every place that told readers reduced motion was their responsibility, plus one inverted example comment and a
  recommended global !important animation reset.
• interact-documentation-site.md is deliberately unchanged. Its rewrite is specified in interact-documentation-site-audit.md §1.5,
  with per-location edits under §3.13, §3.14, M8, §5.6 and §11.

Notes for reviewers

• This is a behavior change (minor bump, 2.6.0): pages that animate today for visitors who prefer reduced motion will stop. Restore
  with Interact.forceReducedMotion = false before Interact.create().
• forceReducedMotion's default read value changes false → undefined. Falsy either way, so if (…) / !… are unaffected; only ===
  false changes meaning. Zero internal readers.