Add dark mode support for SweepAlert iOS app

[anamhira47]

Summary

Adds full dark mode support to the SweepAlert SwiftUI app on the unauthenticated map home screen and throughout the UI.

• Removed the forced .preferredColorScheme(.light) lock so the app follows the device appearance
• Introduced SweepTheme with adaptive asset catalog colors (SweepInk, SweepMuted, SweepBlue, SweepBorder)
• Replaced hardcoded text/border colors and white card strokes with theme tokens
• Added an in-app Appearance picker in Settings (System / Light / Dark)
• Updated the widget text colors to use dynamic UIColor providers

Screenshots

Before (light mode — map home, unauthenticated)

After (dark mode — settings + themed UI)

Device verification

• Remote Revyl build succeeded (cursor-r-0ac20a4e5baf45a88e98263575a09786-e66b40-20260628-055208)
• Device instruction to enable system Dark Mode: success
• Dark mode renders with dark map, dark card surfaces, and light readable text on the settings screen
• Signed-out panel sign-in button aligned to brand blue (sweepBlue)

Test plan

• Revyl remote iOS build passes
• Light mode map home renders correctly (screenshot)
• Dark mode renders with adaptive colors (screenshot + device instruction)
• Appearance picker added in Settings for System/Light/Dark override