feat: add TRON GasFree support to x402 Gateway 1.0.1

[boboliu-1010]

Summary

• use the released x402 SDK 1.0.1 packages
• advertise TRON exact + Permit2 and exact_gasfree payment requirements
• require canonical TRON CAIP-2 network identifiers
• preserve PAYMENT-RESPONSE after settlement when upstream delivery fails
• reject explicit facilitator settlement failures even when transaction metadata is present
• propagate facilitator rate limits and validate production configuration
• protect admin endpoints, isolate metrics per instance, and strip spoofed x402 upstream headers
• support an externally configured absolute payment resource URL

Release

• npm beta: @bankofai/x402-gateway@1.0.1-beta.6
• test image: bankofai/x402-gateway:test

Validation

• npm test (25/25)
• npm pack --dry-run
• npm audit --omit=dev (0 vulnerabilities)
• published package dependencies verified against x402 SDK 1.0.1

Notes

• SunPump upstream HTTP 405 is intentionally out of scope.
• Automated compensation/refund for settled payments with failed upstream delivery remains follow-up work.

[boboliu-1010]

Superseded by #4, which now contains the complete Gateway 1.0.1 feature and public API change set against main.