refactor(layout): extract IOS_TAB_BAR_HEIGHT to shared constants

- Create constants/layout.ts with IOS_TAB_BAR_HEIGHT constant
- Add getTabBarScrollPadding() helper function for common scroll padding pattern
- Update profile.tsx, tasks.tsx, and steps/[id].tsx to use shared constant
- Eliminates duplicate constant definitions across three files

Author: BillChirico

app/(tabs)/profile.tsx

@@ -34,13 +34,7 @@ import { logger, LogCategory } from '@/lib/logger';
 import { formatDateWithTimezone, parseDateAsLocal, getUserTimezone } from '@/lib/date';
 import SettingsSheet, { SettingsSheetRef } from '@/components/SettingsSheet';
 import LogSlipUpSheet, { LogSlipUpSheetRef } from '@/components/sheets/LogSlipUpSheet';
-
-// =============================================================================
-// Constants
-// =============================================================================
-
-/** Standard iOS tab bar height (49pt) - used for scroll padding */
-const IOS_TAB_BAR_HEIGHT = 49;
+import { getTabBarScrollPadding } from '@/constants/layout';
 
 // =============================================================================
 // Helper Components
@@ -173,7 +167,7 @@ export default function ProfileScreen() {
   // Get safe area insets for scroll padding
   const insets = useSafeAreaInsets();
   // Account for native tab bar height on iOS
-  const scrollPadding = Platform.OS === 'ios' ? insets.bottom + IOS_TAB_BAR_HEIGHT + 16 : 16;
+  const scrollPadding = getTabBarScrollPadding(insets.bottom);
   const settingsSheetRef = useRef<SettingsSheetRef>(null);
   const logSlipUpSheetRef = useRef<LogSlipUpSheetRef>(null);
   const scrollViewRef = useRef<ScrollView>(null);

app/(tabs)/steps/[id].tsx

@@ -20,13 +20,7 @@ import { supabase } from '@/lib/supabase';
 import { StepContent, UserStepProgress } from '@/types/database';
 import { logger, LogCategory } from '@/lib/logger';
 import { trackEvent, AnalyticsEvents } from '@/lib/analytics';
-
-// =============================================================================
-// Constants
-// =============================================================================
-
-/** Standard iOS tab bar height (49pt) - used for footer padding when nested in tabs */
-const IOS_TAB_BAR_HEIGHT = 49;
+import { getTabBarScrollPadding } from '@/constants/layout';
 
 // =============================================================================
 // Component
@@ -486,7 +480,7 @@ const createStyles = (theme: ThemeColors, insets: { top: number; bottom: number
     },
     bottomPadding: {
       // Account for native tab bar height plus safe area so content isn't hidden
-      height: Platform.OS === 'ios' ? insets.bottom + IOS_TAB_BAR_HEIGHT + 16 : 24,
+      height: getTabBarScrollPadding(insets.bottom, Platform.OS === 'ios' ? 16 : 24),
     },
     navigation: {
       flexDirection: 'row',

app/(tabs)/tasks.tsx

@@ -28,13 +28,7 @@ import { formatProfileName } from '@/lib/format';
 import { logger, LogCategory } from '@/lib/logger';
 import { parseDateAsLocal } from '@/lib/date';
 import { trackEvent, AnalyticsEvents } from '@/lib/analytics';
-
-// =============================================================================
-// Constants
-// =============================================================================
-
-/** Standard iOS tab bar height (49pt) - used for FAB positioning */
-const IOS_TAB_BAR_HEIGHT = 49;
+import { IOS_TAB_BAR_HEIGHT } from '@/constants/layout';
 
 // =============================================================================
 // Types & Interfaces

constants/layout.ts

@@ -0,0 +1,33 @@
+// =============================================================================
+// Layout Constants
+// =============================================================================
+// Shared layout constants used across the app for consistent spacing and sizing
+
+import { Platform } from 'react-native';
+
+/**
+ * Default iOS tab bar height in points.
+ * Used to calculate safe scroll padding when content appears above the tab bar.
+ *
+ * @remarks
+ * This value matches the standard UITabBar height (49pt) on iOS.
+ * On Android, the navigation bar height varies and is handled differently.
+ */
+export const IOS_TAB_BAR_HEIGHT = 49;
+
+/**
+ * Calculates the bottom padding needed for scrollable content above the tab bar.
+ *
+ * @param bottomInset - The bottom safe area inset from useSafeAreaInsets()
+ * @param extraPadding - Additional padding to add (defaults to 16)
+ * @returns The calculated padding for iOS, or extraPadding for other platforms
+ *
+ * @example
+ * ```tsx
+ * const insets = useSafeAreaInsets();
+ * const paddingBottom = getTabBarScrollPadding(insets.bottom);
+ * ```
+ */
+export function getTabBarScrollPadding(bottomInset: number, extraPadding: number = 16): number {
+  return Platform.OS === 'ios' ? bottomInset + IOS_TAB_BAR_HEIGHT + extraPadding : extraPadding;
+}