feat: add network detection and switching (#69)

[sheyman546]

Summary

Implements issue #69 — network detection and switching for SubTrackr.

Changes

• src/hooks/useNetwork.ts — useNetwork hook wrapping useNetworkStore, auto-initializes on mount, exposes switchNetwork, checkHealth, refreshNetworks
• src/components/common/NetworkSwitcher.tsx — UI component listing Stellar/EVM networks with tap-to-select, testnet badges, and accessibility roles
• src/screens/NetworkSettingsScreen.tsx — screen showing active network, the switcher, and an on-demand health check
• src/navigation/types.ts — added NetworkSettings route
• src/navigation/AppNavigator.tsx — registered NetworkSettingsScreen in SettingsStack
• src/screens/SettingsScreen.tsx — added Network Settings link

Tests

24 new tests across 2 suites, all passing:

• src/hooks/__tests__/useNetwork.test.ts (11 tests)
• src/services/__tests__/networkService.test.ts (13 tests)

What was tested

• Lint: clean
• Unit tests: 24/24 pass
• No conflicts with existing code
  closes 🔧 Fix getUpcomingSubscriptions performance #64

[sheyman546]

please i have tried all i could please help me merge this issue the issue on the ci test is not what i an fix

[Smartdevs17]

⚠️ Merge failed — could not merge.

Possible reasons:

• CI checks not passing
• Branch protection rules
• Other merge requirements not met

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[sheyman546]

boss can i be awarded please

[Smartdevs17]

boss can i be awarded please

Go and check the drips guidelines for reward. Thank you for contributing to the project. Do well to leave a review 🙏