refactor: extract player components, add stack headers, add tests

- Extract player UI into src/features/player/ components (TimerRing, BurnBar, etc.)
- Add transparent stack headers for workout/[id] and program/[id] screens
- Refactor workout/[id], program/[id], complete/[id] screens
- Add player feature tests and useTimer integration tests
- Add data layer exports and test setup improvements

app/_layout.tsx

@@ -119,6 +119,13 @@ function RootLayoutInner() {
             <Stack.Screen
               name="workout/[id]"
               options={{
+                headerShown: true,
+                headerTransparent: true,
+                headerBlurEffect: colors.colorScheme === 'dark' ? 'dark' : 'light',
+                headerShadowVisible: false,
+                headerTitle: '',
+                headerBackButtonDisplayMode: 'minimal',
+                headerTintColor: colors.colorScheme === 'dark' ? '#FFFFFF' : '#000000',
                 animation: 'slide_from_right',
               }}
             />
@@ -128,6 +135,19 @@ function RootLayoutInner() {
                 animation: 'slide_from_right',
               }}
             />
+            <Stack.Screen
+              name="program/[id]"
+              options={{
+                headerShown: true,
+                headerTransparent: true,
+                headerBlurEffect: colors.colorScheme === 'dark' ? 'dark' : 'light',
+                headerShadowVisible: false,
+                headerTitle: '',
+                headerBackButtonDisplayMode: 'minimal',
+                headerTintColor: colors.colorScheme === 'dark' ? '#FFFFFF' : '#000000',
+                animation: 'slide_from_right',
+              }}
+            />
             <Stack.Screen
               name="collection/[id]"
               options={{