docs: document swarm/agent/updater APIs and add PKI-and-mTLS reference
- Module-Reference-Workers: new sections for decnet/swarm/, decnet/agent/,
and decnet/updater/ covering exported symbols, FastAPI routes, uvicorn
launcher flags, and the executor seams the test suite monkeypatches.
- PKI-and-mTLS: standalone developer page covering CA generation, leaf
issuance, SSLContext wiring (client + server), the VERIFY_X509_STRICT
workaround for Python 3.13, the RFC 5425 log pipeline's reuse of the
same CA, and the currently-unenforced CN/role-separation gap.
- Sidebar: link the new PKI page from the Developer docs section.
