feat: add WalletConnect support

[newmattock]

Fixes #2

Summary

• add WalletConnect v2 support through the Stellar Wallets Kit WalletConnect adapter
• add a wallet selection modal with Freighter and WalletConnect options from the Connect Wallet button
• keep the existing WalletContext connect/sign/disconnect surface usable for existing callers while routing signatures through the active provider
• persist provider choice, clear expired WalletConnect sessions on signing failure, and show configuration guidance when NEXT_PUBLIC_WALLETCONNECT_PROJECT_ID is missing
• include focused tests for provider selection, WalletConnect disabled/configured states, and existing connected wallet states
• include current-main build fixes for governance status config, federation typing, and evidence hashing

Validation

• npm test -- src/components/tests/WalletButton.test.tsx src/components/tests/WalletSelectionModal.test.tsx --reporter verbose
• npm run lint -- src/context/WalletContext.tsx src/components/WalletButton.tsx src/components/WalletSelectionModal.tsx src/utils/walletConnect.ts src/components/tests/WalletButton.test.tsx src/components/tests/WalletSelectionModal.test.tsx app/governance/page.tsx src/utils/federation.ts src/utils/evidence.ts
• npm run build
• git diff --check
• local HTTP smoke: HEAD / returned 200 on port 3025

Notes

WalletConnect pairing requires NEXT_PUBLIC_WALLETCONNECT_PROJECT_ID. When it is absent, the UI keeps Freighter available and explains the missing configuration.