Archive the advertise-valid-ipps-certificate change

Moves the completed change to
openspec/changes/archive/2026-10-18-advertise-valid-ipps-certificate/ and syncs
the printserver/cups capability into openspec/specs/: the image dependency
requirement now mentions the TLS tooling, and two requirements are added for the
name-valid _ipps certificate and for starting cleanly on stale runtime state.

openspec/changes/archive/2026-10-18-advertise-valid-ipps-certificate/.openspec.yaml

@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-10-18