Optimize Rendering (Redraws / Recomposition)

Background: Native [platform] app. iOS uses SwiftUI; Android uses Compose.
The screen redraws/recomposes too much or animates with jank: [describe
the screen and what triggers the churn].

Use case: Reduce unnecessary view updates so the screen renders only when
it truly needs to.

Implementation details:
- iOS: minimize what each view body depends on; split large views so a
  small state change doesn't invalidate everything; stable identity for
  lists; avoid creating new closures/objects in body that defeat
  diffing; use @Observable scoping wisely.
- Android: diagnose recomposition (Layout Inspector recomposition counts);
  ensure stable parameters and immutable types; hoist state correctly;
  use remember/derivedStateOf and keys; avoid reading state too high in
  the tree; watch unstable lambdas.
- Confirm with the tool that updates dropped after the change
- Don't micro-optimize screens that aren't actually hot

Deliverable: The specific causes of over-rendering for this screen, the
fixes per platform, how to measure the redraw/recomposition reduction,
and which parts weren't worth optimizing.