Add sample PQC readiness perspective for CBOM

[bhess]

Adds a sample perspective demonstrating how the perspective model can apply in a CBOM context, using PQC readiness as the example. It lives in a new perspectives/ folder, as discussed in the last Cryptography WG meeting.

The mappings also exercise a proposed expectation field (values are present or absent) on perspective mappings that turns a descriptive mapping into a machine-checkable assertion. That field is not yet in the 2.0 schema, so the sample is illustrative pending that discussion.

[Mehrn0ush]

Hi,
I was reading this PR against #947.

Since changeMechanism is now an array, would “includes runtime-config” fit the rationale better than “runtime-config or restart-required”? Multiple values now mean required steps rather than alternatives.

And if #947 lands first, I assume the path should move from cryptoProperties.agility to component.agility — is that right?

The inventory/algorithm/agility split makes sense to me. One thing I wondered: should primitive: "unknown" / "other" be treated like missing primitive for the inventory check? And whether protocol cipher suites or cert->signing-algorithm linkage are in scope for a later revision.

I also couldn't find perspective-expectation-rationale.md in this PR — is it planned elsewhere, or should the reference in the description come out for now?