Clarify Android local IP HTTPS login failures

[ZacharyZcR]

Summary

• detect native login fetch failures for HTTPS local-network IP URLs
• show an actionable certificate/local-network message instead of a generic "Unexpected error during login user: Network request failed"
• export the Android network security XML so the existing verification script can validate the generated trust-anchor config

Fixes Termix-SSH/Support#881.

Tests

• git diff --check
• npm run verify:android-network-security
• npx eslint app/main-axios.ts plugins/withNetworkSecurityConfig.js (0 errors, existing warnings remain)
• npx tsc --noEmit (fails on existing unrelated repo issues: missing expo-web-browser, WarpgateDialog toast callable type, TunnelManager optional endpointHost type)

Notes

This keeps TLS verification intact. For HTTPS over a local IP, the server certificate still needs to be trusted by Android and valid for that IP address, or the user should use the FQDN with a valid certificate.