v0.1.8: 0.1.8: the OCI stack, certified

Stack only -- no library change. The version bump exists so the Deploy to
Oracle Cloud button stops handing people the 0.1.7 stack, which could not
apply at all.

verify.sh reached 6/6 CERTIFIED on a live tenancy: plan, apply, the MCP
endpoint answering, the instance reaching the database, and keyless
cataloguing through OCI Generative AI. Sixteen objects reflected out of the
stack's own Autonomous Database over one-way TLS, every description written by
Oracle's model with no API key and nothing leaving the tenancy.

Nine applies to get there. The CHANGELOG lists what each one found; all
twenty-one invariants in tests/test_oci_stack.py came from a real failure, not
from imagination.

Also: pyyaml is declared in the dev extra. tests/test_oci_stack.py has parsed
cloud-init.yaml since before tonight and was relying on whatever the runner
happened to have installed.