new web: omnibus build/organization/perf fixes

[patosullivan]

• Resolved build failures in web environment caused by:
  • Incorrect import of react-native-branch through useHandleLogout
  • Direct usage of nativeDb.resetDb instead of platform-specific implementation in useConfigureUrbitClient
  • Build failure due to top-level await causing regeneratorRuntime errors
• Moved signupContext to mobile-specific directory as it's only used in mobile flows
• Resolved CPU-intensive performance issue in ChatList:
  • Replaced useStyle hook with static style object
  • Now using getTokenValue helper to access tamagui's $l padding value
  • Prevents FlashList from freezing app due to excessive re-renders