feat: add Solana invoice guard plugins

[YoungblutSchilling]

Solana Invoice Guard

Adds two composable, least-privilege ZeroClaw tool plugins for Solana invoice workflows:

• solana-pay-request (T1 / build-only): creates canonical Solana Pay transfer URIs without accessing a wallet, signing, or touching the network.
• solana-payment-verify (T0 / read-only): verifies finalized or confirmed SOL and SPL invoice payments from transaction data. It validates recipient net balance delta, transaction success, mint, reference, memo, and exact/at-least amount policies.

Security and reliability

• Explicitly fail-closed handling for malformed RPC responses and SPL decimal precision above 19.
• RPC endpoint hardening rejects credentials, localhost, reserved/private/special IP literals, query strings, and fragments.
• No wallet access, signing, funds movement, or broad host permissions.

Validation

• 21 host tests passing (8 request + 13 verification)
• cargo clippy passes for both plugins
• wasm32-wasip2 release builds pass
• Registry metadata validation passes
• Verified against a real finalized Solana mainnet transaction:
  • tx: 2BwJJ2vHxqHuRJLa2W3aTu9SqLsqqSAiRuiDUf1yGVYkSeyEyry7HdwBvLxaFC9LUMk2oWpqSxeZGz9ioqXWqJxX
  • result: paid, valid=true, 0.0013 SOL

Each plugin includes a standalone README, manifest, pure Rust core, thin WASM component shim, and host-run tests.