Wallet truth pass

[epicexcelsior]

Summary

• Route SOL balance and send submission through the selected RPC adapter.
• Replace the hardcoded review fee with a live devnet fee estimate.
• Centralize demo mode configuration and remove simulated transfer success.
• Improve wallet denial and no-route states with retryable review UI.

Deviations / notes

• Based on current upstream v3, not the fork-local polished branch.
• No SPL token transfer support is added; non-SOL transfers now fail honestly instead of showing a simulated success.
• Mesh relay submission is only attempted when an active relay beacon exists. No beacon bridge or peer public-key mapping is added here.
• The simple SOL transfer fee still often displays 0.000005 SOL; that is expected because devnet reports 5000 lamports for a one-signature transfer, but the value is now fetched from RPC.
• This PR can merge independently, but final manual smoke should include one online devnet SOL send.

Validation

• npm run lint
• npx tsc --noEmit currently fails on upstream/v3 baseline LXMF type errors in context/LxmfContext.tsx and src/hooks/useNetworkMode.ts.
• Fee probe against devnet returned 5000 lamports for simple SOL transfers.

Manual checks before merge

• Online device: route shows Online RPC and tiny devnet SOL send returns a signature.
• Deny wallet approval once, then Try again opens wallet approval again.
• Demo mode off has no recipient prefill; demo mode on pre-fills the devnet recipient.