docs(muninn-gate): Dockerfile comment — dispatch pin now 0.1.5, SHA-tag note

Gate rebuilt off vh/muninn-gate main (bc04c4c) for the muninn-dispatch
0.1.4->0.1.5 bump (concept_schema/concept_schema_source row fields). Gate
version unchanged at 0.0.14; note to also tag the image with the source SHA
for traceability, and that the pin is authoritative in pyproject.

stacks/muninn-gate/Dockerfile

@@ -1,11 +1,14 @@
 # muninn-gate — WG-internal HTTP front door for the Muninn ingestion queue (#377).
 # No Dockerfile in the upstream repo (vh/muninn-gate); this is infra-ops's.
-# muninn-dispatch==0.1.4 comes from the internal Gitea PyPI index "gitea";
-# the read token is passed as a BuildKit secret (never baked into a layer).
+# muninn-dispatch is pinned in pyproject (currently ==0.1.5, from vh/muninn-gate
+# main; bumped from 0.1.4 for the concept_schema/concept_schema_source fields)
+# and comes from the internal Gitea PyPI index "gitea"; the read token (vh) is
+# passed as a BuildKit secret (never baked into a layer). Also tag the image with
+# the source SHA for traceability, since the gate version (0.0.14) is unchanged.
 #
 #   DOCKER_BUILDKIT=1 docker build \
-#     --secret id=gitea_pw,src=<read-token-file> \
-#     -t muninn-gate:0.0.14 .
+#     --secret id=gitea_pw,src=<vh-token-file> \
+#     -t muninn-gate:0.0.14 -t muninn-gate:<src-sha> .
 FROM python:3.11-slim
 
 RUN pip install --no-cache-dir uv==0.11.* \