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, and it sits too high in the header instead of being bottom-aligned. Android is unaffected.

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 (less visible).

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
• ⚠️ Marked draft pending manual verification on an iOS simulator (example app → Appbar screen → cycle small/medium/large/center-aligned; confirm the title is fully visible and bottom-aligned in medium/large, and there's no Android regression). If alignSelf: 'stretch' alone isn't sufficient, follow-ups would be giving controlsRow a fixed height instead of flex: 1, and/or rebalancing the v3MediumContainer / v3LargeContainer paddings in AppbarContent.tsx.

[callstack-bot]

Hey @azizbecha, thank you for your pull request 🤗. The documentation from this branch can be viewed here.