feat(x402): add multi-network payments with Permit2, Solana and NEAR

[Revinand]

Summary

Extend x402 beyond Base with built-in and configurable EVM networks, Permit2, Solana and NEAR token payments. Resources can define their own offers, selected before verification and settlement.

• Expose offer details and health through discovery, readiness, CLI diagnostics and the dashboard.
• Distinguish rejected payments from uncertain settlement outcomes; support safe retries and preserve replaced payment attempts.
• Harden address, authorization, currency, RPC and facilitator validation.
• Bound facilitator waits and return retryable overload and outage errors.
• Settle MPP payments before backend execution by default.
• Split large modules and protocol docs; add examples, migration guidance, offline settlement tests and public-network smoke harnesses.

Migration

Local Anvil now uses eip155:31337. See docs/migration-2.1.md for configuration, settlement-order and type changes.