chore: address low-risk Copilot AI findings (comments and strings) (#556)

* chore: address low-risk Copilot AI findings (comments and message strings)

Cosmetic, non-behavioral changes from the AI code-quality findings:
- metpo.Makefile diff-release: 'ERROR'/'WARN' -> 'Error'/'Warning' in echo
  messages for consistent capitalization.
- metpo-edit.owl: clarify the obsolescence-reason comment that the IAO code
  assignment is tracked in issue #521.
- qc-positive-fixture.ttl: note that metpo:1000000 / metpo:2000000 are
  intentional fixture-only replacement IRIs, not production terms.

Behavioral findings (cross_ontology_search.py, run_sparql_metatest.sh) are
intentionally left for separate review.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* chore: move QC-fixture comment to the METPO prefix-normalization PR

The fixture explanatory comment belongs with the work that normalizes that
file's metpo: -> METPO: prefix (issue #16), so it is re-added there in the
canonical uppercase form. This PR keeps only the Makefile and OWL findings.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: turbomam

src/ontology/metpo-edit.owl

@@ -61,7 +61,7 @@ AnnotationAssertion(rdfs:label IAO:0000231 "has obsolescence reason")
 
 AnnotationAssertion(rdfs:label IAO:0100001 "term replaced by")
 
-# Obsolescence reason values (display labels; correct code ASSIGNMENT is tracked in #521)
+# Obsolescence reason values (display labels; correct IAO code assignment for these obsolescence reasons is tracked in issue #521)
 
 AnnotationAssertion(rdfs:label IAO:0000226 "placeholder removed")
 AnnotationAssertion(rdfs:label <http://purl.obolibrary.org/obo/OMO_0001000> "out of scope")

src/ontology/metpo.Makefile

@@ -92,12 +92,12 @@ diff-sheets:
 
 # Diff current working templates against the last tagged release
 diff-release:
-	@command -v uv >/dev/null 2>&1 || { echo "ERROR: 'uv' is required for diff-release (host-only target)."; exit 1; }
-	@command -v git >/dev/null 2>&1 || { echo "ERROR: 'git' is required for diff-release."; exit 1; }
-	@git rev-parse --is-inside-work-tree >/dev/null 2>&1 || { echo "ERROR: diff-release must be run from within a git work tree."; exit 1; }
+	@command -v uv >/dev/null 2>&1 || { echo "Error: 'uv' is required for diff-release (host-only target)."; exit 1; }
+	@command -v git >/dev/null 2>&1 || { echo "Error: 'git' is required for diff-release."; exit 1; }
+	@git rev-parse --is-inside-work-tree >/dev/null 2>&1 || { echo "Error: diff-release must be run from within a git work tree."; exit 1; }
 	@release_ref=$$(git describe --tags --abbrev=0 2>/dev/null); \
 	if [ -z "$$release_ref" ]; then \
-		echo "WARN: No git tags found; falling back to 'main'."; \
+		echo "Warning: No git tags found; falling back to 'main'."; \
 		release_ref=main; \
 	fi; \
 	cd ../.. && uv run diff-templates -a "$$release_ref" -b HEAD --cell-diffs