docs(akroasis): correct Sphragis verification profile

[forkwright]

Summary

• use the producer-side preview-pq,hazmat profile so the exact Sphragis checkout executes its full known-answer and conformance targets
• state explicitly that producer test reachability does not permit Akroasis consumers to enable or call hazmat
• classify the two living reference-encryption boundary documents as non-evergreen while preserving authored ownership

Tracker disposition

Refs #395.
Refs forkwright/sphragis#43.

Both trackers remain open; this documentation correction does not claim a reviewed consumer handoff.

Verification

• git diff --check
• docs/MANIFEST.toml parsed successfully with Python tomllib
• exact-value inspection of the changed command and manifest entries
• no local build, test, or gate command was run, per operator direction

Base and collision check

• based on live main at 1451b4c
• release PR chore(main): release 0.6.2 #465 changes only .release-please-manifest.json, CHANGELOG.md, Cargo.lock, and Cargo.toml; it remains path-disjoint from this two-document patch