dav1dprometheus 2026-05-09: line 284 internal-consistency fix

The doc's own meta-comment at line 160 explicitly distinguishes
witnesses (kernel/cache/LLM channels over the same canonical bytes)
from carriers (text/image/audio/world modalities). Line 284 still
used the conflated phrase 'multi-modality witness' that the meta-
comment was teaching against.

Update to 'multi-witness canonical-agreement' — consistent with
the doc's own clarification, with David's 2026-05-10 review of
#000037 (which renamed #000028's mechanism descriptor across the
controller spec for the same precision reason), and with the
2026-05-10 #000006 amend that uses the corrected vocabulary.

Closed-ticket references to #000028 by its actual title (Multi-
modality witness for canonical shapes) are intentionally not
touched — those are accurate citations of the ticket title, not
generic mechanism descriptors.

Doc-only update; no schema, no governance hash, no code change.

docs/dav1dprometheus-update-2026-05-09.md

@@ -281,8 +281,8 @@ A new kernel landed today: tighter sibling of
 result that isn't a non-negative `sp.Integer` raises
 `PiStarError`. Plain decimal output (`b"10"`); composes with
 `arithmetic@v1` for byte-identical agreement (`b"10/1"`) so the
-multi-modality witness can pin equivalence-class agreement when
-both routes fire on the same question.
+multi-witness canonical-agreement pipeline can pin equivalence-
+class agreement when both kernel routes fire on the same question.
 
 The 16-kernel registry now covers: text → claim_lattice → code →
 arithmetic → logic → time-series → tabular → symbolic-algebra →