feat: add horizontal pager for swipe navigation between tabs

[jvsena42]

Summary

Add swipe gesture navigation between tabs using HorizontalPager on Android and TabView with .page style on iOS. The bottom bar is lifted out of individual screens into the root App/iOSApp so it stays fixed while page content swipes underneath.

Changes

• Replace when/mutableStateOf tab switching in App.kt with HorizontalPager inside a Box layout, with WornBottomBar overlaid at the bottom
• Replace switch tab switching in iOSApp.swift with TabView(.page) and WornBottomBar placed outside the TabView
• Remove WornBottomBar from all 5 screen Scaffolds (Android) and all 5 screen views (iOS)
• Clean up unused onTabSelected parameters from scaffold-level functions
• Add bottom padding to the Wardrobe FAB so it sits above the overlaid bottom bar
• Set BgPage background on the root Box to prevent white showing behind the bottom bar

Test plan

• Swipe left/right between all 5 tabs — animation should be smooth and bottom bar should remain fixed
• Tap bottom bar tabs — should animate to the correct page
• Verify the bottom bar active indicator follows both swipe and tap navigation
• Verify the Wardrobe FAB is fully visible above the bottom bar
• Cross-tab navigation still works (e.g., "Go to Settings" from Try It and Gaps screens)
• Test on both phone and tablet form factors

Checklist

• ./gradlew detekt passes
• Tested on Android
• Tested on iOS
• Updated documentation (if applicable)