perf(ui): isolate tab strip spring rebuilds (Fluid F1)

[ZhuchkaTriplesix]

Parent

Part of #356 · Fluid perf audit F1 (P0)

Problem

QueryaTabStrip wraps the entire Stack (indicator + all tab Focus/Gesture/AnimatedContainer rows) in a ListenableBuilder with no child:. Dual QueryaSpringControllers (_indicatorLeft / _indicatorWidth) can notify twice per vsync, rebuilding every tab every spring tick.

Where: lib/shared/widgets/querya_tab_strip.dart

Expected

• Tab row is stable across indicator ticks (ListenableBuilder.child or equivalent)
• Only the sliding pill animates / rebuilds
• Pill wrapped in RepaintBoundary
• Prefer a single notify path when both springs move

Acceptance

• Indicator animation no longer rebuilds all tab widgets each tick
• Widget test covering indicator redirect still passes
• Brief note in PR why rebuild scope is isolated

Related

• Epic Fluid: epic(ui): Fluid morphing — evolve QueryaMotion (post-0.4.11 shell) #342
• Checklist: docs/perf-baseline.md §10 Tab strip

[ZhuchkaTriplesix]

Fixed and merged via PRs #367/#368/#369 on dev.