[Adedayo0101]

Summary

Reject unsupported NEXT_PUBLIC_NETWORK values during config module initialization instead of silently selecting testnet settings. Valid testnet and mainnet configurations keep their corresponding passphrases and default RPC URLs.

Linked issue

Closes #515

What was tested

• Focused configuration test: npx vitest run lib/config-rpc.test.ts --config vitest.issue-515.config.mts — passed, 3 tests. This used a temporary setup-free config because the repository Vitest setup cannot resolve the missing @testing-library/react dependency; the temporary file was removed.
• Focused TypeScript check for lib/config.ts — passed.
• Changed-file ESLint — passed.
• npm run lint — passed with 7 existing warnings.
• npm run typecheck — failed because dependencies are missing from node_modules: @testing-library/react and @next/bundle-analyzer.
• npm test — failed before collecting tests because the global Vitest setup imports missing @testing-library/react (103 test files affected).
• npm run build — failed loading next.config.ts because @next/bundle-analyzer is missing.

Offline dependency restoration was attempted without changing package manifests or the lockfile, but could not complete because the npm cache lacks duplexer.

Checklist

• npm test passes
• npm run typecheck passes
• npm run lint passes
• Tested locally in the browser (where the change touches UI)