fix(theme): provide nav theme so expo-router 57 keeps glass transparent

[RonenMars]

Problem

Selecting Apple Glass → Aurora renders a flat light-grey screen instead of the aurora gradient once expo-router is bumped past 57.0.2 (dependabot PR #293, currently open, reproduced on the 2026-07-11 integration branch).

expo-router 57.0.3 (upstream expo/expo#47121, an iOS swipe-back white-flash fix) started painting the native stack container with the react-navigation theme's colors.background:

• build/react-navigation/native-stack/views/NativeStackView.native.js: <ScreenStack nativeContainerStyle={{ backgroundColor: colors.background }}>
• → react-native-screens RNSScreenStack.mm: UINavigationController.view.backgroundColor (iOS-only)

The app never provided a react-navigation theme, so the container falls back to DefaultTheme's opaque rgb(242,242,242) — covering the glass gradient rendered behind the <Stack> in app/_layout.tsx.

Fix

Wrap the Stack in expo-router's re-exported ThemeProvider, based on DefaultTheme/DarkTheme per app color mode, overriding only colors.background:

• glass → 'transparent' (the gradient shows through the native container)
• non-glass → theme.bg.primary (also upgrades the iOS swipe-back gap from white/grey to the theme background)

This adopts the public react-navigation theming contract — the exact mechanism the upstream change was designed around. On expo-router 57.0.2 (current main) the container prop doesn't exist yet, so the provider is a behavioral no-op there: this PR can merge before #293 and glass never breaks.

Test

__tests__/unit/components/themed-stack-nav-theme.test.tsx renders ThemedStack (now a named export) and asserts the nav theme it provides, plus the Stack contentStyle, for glass / dark / light themes against the real vendored DefaultTheme/DarkTheme. Falsified against the regression: with the override removed it fails with the literal bug value (rgb(242, 242, 242)).

Support changes: \.css$ jest moduleNameMapper entry + __mocks__/style-mock.js, because the test imports app/_layout.tsx, which imports global.css.

Verification

• New test 3/3 green; 3/3 red with the fix reverted (exact regression values)
• Full unit suite green (54/54 suites, 513/513 tests on expo-router 57.0.2)
• TypeScript clean

Merge order

Land this before (or together with) #293 — inert on 57.0.2, required on ≥57.0.3.

[RonenMars]

Superseded by #297, which carries the identical nav-theme fix plus the synced ios/Podfile.lock for the 57.0.4 / camera 57.0.1 / worklets 0.10.2 bumps.