Custodian Kernel 0.4.3

Custodian Kernel 0.4.3 adds a vendor-neutral PaymentProcessor interface (custodian.processors.base) so a payment vendor integration no longer needs to be bundled with the kernel to work with it, shared crash-safe ledger primitives (custodian.authority.ledger) available to any processor implementation, and importlib.metadata entry-point discovery so a separately-installed package can register its own skills and setup components with zero kernel code changes. The kernel is now mechanically forbidden from importing any payment vendor SDK directly. The exact attached wheel and source archive passed the full 3,000+ test suite, the complete custodian-release.py prepare battery (fresh install, upgrade from the real published 0.4.2, managed two-slot install/reinstall/uninstall with data preservation, PEP 668 compliance), a real end-to-end behavioral simulation against dashboard/api/operator.py's full demo arc compared side by side with 0.4.2, and a genuine TestPyPI upload-and-install round trip. Not yet published to the real PyPI index.