PRA-001 T12: agent-trace terms/provider tagging + provider/channel-excluding pool rebuild (P-TERMS) #4446

PRA-001 T12 (spec §2.10, §9 P-TERMS; K̂ 60 min). Owner per brief: aprender-a2; implemented by aprender-fb on a branch off rex/001 for a2 to fold.

Every agent-trace-v1 row carries provider, exact model_id, access_channel, terms_ref {url, effective_date, fetched_at}. Deliverable:

• crates/aprender-review-experiment/src/terms.rs: validate the four fields (unknown/alias/mismatch = gap, row RED), and rebuild(rows, Exclude) with first-class --exclude-provider / --exclude-channel args; rows with gaps are refused by every rebuild; Exclude::public_release() = local only.
• Contract agent-trace-terms-v1 with falsifiers planted RED first.

Acceptance (P-TERMS): a pool rebuild excluding one provider succeeds with 0 rows of that provider.

Not legal advice; S-6 governs. No transcripts or trace blobs in this repo.

Refs #4354