docs: add TRUST-DEFAULTS-POLICY and the trust/adjust defaults handover prompt

TRUST-DEFAULTS-POLICY.adoc codifies the 2026-09-02 ruling that every repo
ships best-of-best security defaults (Trustfile) and accessibility
defaults (Adjustfile), blanked only through `just strip-rsr-defaults`.
It carries the DNS/email/TLS/PQ control list, the headers ratchet, the
permissions dead man's handle, the badge rule and the robustifier split.

docs/handover/2026-09-02-trust-adjust-defaults-session-prompt.adoc is the
prompt for the separate session that owns the accessibility policy, the
exemplar Trustfile gap-fill, the PORT-REGISTRY prose and the template
strip family. Both files existed only on one machine until this commit.

Author: hyperpolymath