feat: support card payments and payment recovery

[nkavian]

Summary

• Add Stripe SPT Seller and Visa CARD Buyer/Seller support through the existing MPP APIs.
• Add explicit instrument selection and offer handling, matched settlement receipts, and payment-status recovery without creating replacement payments.
• Extend runnable examples, installation checks, and integration tests across the supported payment methods.
• Run the shared payment-status, Stripe, and CARD suites alongside the existing suites.

Upstream limitation

pympp 0.11.0 drops challenge.description when parsing credentials (pympp#272). The conformance report retains the failed preservation case. CI accepts only that exact failure, with a companion check proving the same operation succeeds when only the description and its platform echo are omitted. Other failures, an upstream version change, or an unexpected pass block CI. The README explains the integrator impact.

Verification

• make sync verify on Python 3.11, 3.12, 3.13, and 3.14: formatting, types, tests, distribution build, and isolated consumers.
• node --test scripts/conformance.test.mjs and JavaScript syntax checks.
• Shared conformance on all four Python versions, including the documented allowance and existing unsupported subscription cases.

Tests use real upstream middleware and local HTTP servers with controlled platform responses. Live payment execution and publication are outside this PR.