fix(core): add HTTP facilitator transport context

[Bortlesboat]

Summary

• wrap HTTP facilitator transport calls with operation-specific context for verify, settle, and supported
• preserve the original thrown error detail when auth header setup fails before any request is sent
• add regression coverage for fetch rejections and auth-header setup failures in the core HTTP client tests

Notes

Issue #959 already has a Go-oriented facilitator improvement linked in the thread. This PR covers the remaining TypeScript HTTP client failure modes where requests fail before a response body exists.

Testing

• pnpm --dir "C:/Users/andre/.config/superpowers/worktrees/x402/codex-x402-error-messages-959/typescript" --filter @x402/core test -- test/unit/http/httpFacilitatorClient.test.ts
• pnpm --dir "C:/Users/andre/.config/superpowers/worktrees/x402/codex-x402-error-messages-959/typescript/packages/core" exec eslint src/http/httpFacilitatorClient.ts test/unit/http/httpFacilitatorClient.test.ts
• pnpm --dir "C:/Users/andre/.config/superpowers/worktrees/x402/codex-x402-error-messages-959/typescript/packages/core" exec prettier --check src/http/httpFacilitatorClient.ts test/unit/http/httpFacilitatorClient.test.ts

Closes #959

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