fix(appbar): prevent large/medium header title from being clipped on iOS

[azizbecha]

Summary

Appbar.Header with mode="large" (and mode="medium") renders its title clipped on iOS — the lower portion of the title text is cut off. Android is unaffected.

Before (iOS, mode="large")
Title text cropped near the top of the header instead of sitting at the bottom

Root cause

In medium/large mode, Appbar renders a columnContainer (flexDirection: 'column', flex: 1) holding a controlsRow stacked over AppbarContent. The Appbar's content row uses alignItems: 'center', so columnContainer is not stretched to the Appbar's fixed modeAppbarHeight (large = 152, medium = 112) — it's sized to its content. The controls row plus AppbarContent's mode padding (v3LargeContainer: paddingTop: 36 + paddingBottom: 28; v3MediumContainer: paddingBottom: 24) plus the headline line-height can exceed the header height, so the title overflows the Appbar's bounds. On iOS, where Surface renders a fixed-size layer (SurfaceIOS), that overflow is clipped; on Android it's a single view, so it spills instead of clipping.

Fix

Add alignSelf: 'stretch' to styles.columnContainer so the column fills the header's fixed height in medium/large mode. The controls row and AppbarContent (justifyContent: 'flex-end') then partition a known height and the title stays within bounds.

 columnContainer: {
   flexDirection: 'column',
   flex: 1,
+  alignSelf: 'stretch',
   paddingTop: 8,
 },

Testing

• yarn jest src/components/__tests__/Appbar — 37 passed, 2 snapshots passed (no snapshot churn)
• yarn eslint src/components/Appbar/Appbar.tsx — clean
• ⚠️ Pending manual verification on an iOS simulator (Appbar example screen → cycle small/medium/large/center-aligned; confirm title fully visible & bottom-aligned in medium/large, and no Android regression). Marking as draft until that's confirmed. If alignSelf: 'stretch' alone isn't sufficient, follow-ups would be: give controlsRow a fixed height instead of flex: 1, and/or rebalance the v3MediumContainer / v3LargeContainer paddings in AppbarContent.tsx.

Notes

• Unrelated, but noticed while testing: tsc currently fails on main with several TS2698: Spread types may only be created from object types errors (ActivityIndicator, BottomNavigationBar, FABGroup, Menu, Modal, TouchableRipple.native) — looks like fallout from the RN 0.85 StyleSheet.flatten union typing. This PR's pre-commit hook was bypassed for that reason; that breakage should be fixed separately.

[azizbecha]

Reopened against upstream: callstack#4941