UI: Refactor TitleBar back button implementation

[ksharma-xyz]

TL;DR

Simplified title bar navigation by introducing a standardized back button component.

What changed?

• Moved back button implementation from individual screens to the TitleBar component
• Replaced navAction parameter with onNavActionClick callback in TitleBar
• Created a reusable NavActionButton component with consistent styling and behavior
• Removed redundant back button implementations from ServiceAlert, DateTimeSelector, Settings, ThemeSelection, and TimeTable screens

Why make this change?

• Reduces code duplication across multiple screens
• Ensures consistent back button behavior and appearance throughout the app
• Improves maintainability by centralizing navigation UI logic
• Simplifies screen implementations by abstracting navigation details

[ksharma-xyz]

• UI: Replace klickable with scalingKlickable in radio buttons #560
• UI: Add scaling click animation to Button component #559
• UI: Replace clickable with klickable modifier #555
• UI: Move color utilities from trip-planner to TAJ #554
• UI: Create custom ripple effect for Taj #553
• UI: Create Taj Button variants #552
• UI: Refactor alert button and improve button components #551
• UI: Add SubtleButton component to TAJ #550
• UI: Replace SecondaryButton with Text in DateTimeSelector #549
• UI: Refactor TitleBar back button implementation #548 👈 (View in Graphite)
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