WalletConnect v2 integration alongside native wallets

[truthixify]

Tier: L (1-2 weeks) Type: feature

Context

Native Stellar wallets (Freighter, Albedo, xBull, LOBSTR) cover desktop well. WalletConnect v2 brings mobile + multi-wallet bridge to the same flow.

Scope

• Add WalletConnect adapter to the Stellar wallets registry (PR multi-wallet support for stellar solved #49)
• WalletConnect modal alongside native pickers
• Test against at least one WalletConnect-compatible Stellar wallet
• Documentation for adding more WC-compatible wallets

Acceptance criteria

• WC adapter implemented matching StellarWallet interface
• Picker shows WC option
• Mobile-tested with at least one wallet
• Documentation

Files to start with

• src/wallets/stellar/ (extend)
• WalletConnect Stellar docs