feat: initial php server support

[lucasacoutinho]

Description

This PR adds initial PHP server support for the x402 protocol.

Tests

Core Library (php/x402)

cd php/x402 && composer test

24 tests passing covering:

• AmountTest - Currency conversions (decimal ↔ USDC base units)
• NetworkTest - Chain IDs, testnet detection, USDC addresses, custom network registration
• PaymentPayloadTest - Base64 encoding/decoding, validation, error handling
• PaymentRequirementsTest - Requirements creation and serialization

Laravel Package (php/x402-laravel)

cd php/x402-laravel && composer test

52 tests covering:

Unit tests:

• Exception classes and error messages
• PendingPayment fluent builder API

Feature tests:

• DiscoveryTest - Resource registration, pagination, metadata filtering, auto-discovery of paid routes, JSON endpoint responses
• EventsTest - PaymentVerified, PaymentSettled, PaymentFailed event dispatching
• MacrosTest - Route::paid() macro, $request->payer(), $request->requirements() macros
• RequirePaymentMiddlewareTest - 402 responses, header validation, payment verification, settlement flow
• RequirePaymentTest - Full middleware integration with mock facilitator

Manual Testing

Verified the Laravel example app runs successfully:
cd examples/php/servers/laravel && docker compose up

Tested endpoints:

• GET /free - Returns 200 (no payment required)
• GET /weather - Returns 402 with payment requirements
• GET /discovery/resources - Returns discovery JSON

Checklist

• I have formatted and linted my code
• All new and existing tests pass
• My commits are signed (required for merge) -- you may need to rebase if you initially pushed unsigned commits

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[vercel]

@lucasacoutinho is attempting to deploy a commit to the Coinbase Team on Vercel.

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