ui(motion): make Fluid spring honest (real springs vs emphasized)

[ZhuchkaTriplesix]

Parent

Part of epic #477 (fluid motion follow-ups).

Problem

springsEnabled (Full motion) often only selects emphasized cubic curves for dialogs / QueryaFadeSlide / QueryaSwitchingBody. Real SpringSimulation / QueryaSpringController is used mainly for:

• Tab strip indicator
• Split drag settle

Branding says “Fluid spring”; behavior is mixed dialects.

Proposal

Either:

1. Drive shell morphs with QueryaSpringController where interruptible physics helps, or
2. Stop branching on springsEnabled just to pick emphasized — reserve “spring” language for real springs

Document the choice in docs/motion-and-high-refresh.md.

Files

• lib/core/motion/querya_fade_slide.dart
• lib/core/motion/querya_switching_body.dart
• lib/shared/widgets/app_dialog.dart (or dialog enter path)
• lib/core/motion/querya_spring*.dart
• docs/motion-and-high-refresh.md

Acceptance

• Clear rule: when springsEnabled means real physics vs cubic only
• Docs + CONTRIBUTING/motion rule match implementation
• No regression on Reduced / Off

[ZhuchkaTriplesix]

Shipped on dev (PR targeted dev, so auto-close did not fire). See related merged PRs.