UI: Refactor color utilities and add background color helper

[ksharma-xyz]

TL;DR

Improved color handling in the trip planner UI by introducing a new composable function for background colors and making color utility functions private.

What changed?

• Added new backgroundColorOf composable function to handle theme-aware color adjustments
• Made color utility functions (brightenColor, brighten, darkenColor, darken) private
• Simplified color gradient logic in SearchStopScreen by using the new backgroundColorOf function
• Improved code formatting in color conversion functions

How to test?

1. Launch the app and navigate to the trip planner
2. Toggle between light and dark themes
3. Verify that background colors adjust appropriately based on the theme
4. Check that color gradients in the search stop screen appear correctly in both themes

Why make this change?

To encapsulate color manipulation logic and provide a more maintainable, theme-aware approach to handling background colors. This change reduces code duplication and improves the consistency of color handling across the app.

[ksharma-xyz]

• UI: Refactor color utilities and add background color helper #314 👈
• main

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Merge activity

• Nov 7, 3:45 AM EST: Graphite rebased this pull request as part of a merge.
• Nov 7, 3:52 AM EST: A user merged this pull request with Graphite.