fix: close remaining review gaps in vocabulary/deterministic-IRI PR

serialize_to_rdfxml still defaulted entity_type to the bare string
"semantica:Entity" written into an rdf:resource attribute, which isn't
namespace-expanded the way a Turtle angle-bracket or XML element name is -
the same #1101 failure mode, just on the path the original tests didn't
cover. Now uses the full-IRI DEFAULT_ENTITY_TYPE like the Turtle path.

json_exporter.py emits semantica:format and @type: "semantica:KnowledgeGraph",
neither of which was declared in the vocabulary or included in
EMITTED_TERMS, so the "undeclared terms fail the build" guarantee didn't
actually cover them. Both are now declared with rdfs:label/comment and
added to the guard set.

MANIFEST.in didn't mirror the pyproject.toml package-data addition, so a
source-distribution install could ship without the vocabulary file.

The cross-process minting-stability test replaced the subprocess's entire
environment with a POSIX-only PATH, breaking it on Windows and any host
needing other inherited env vars; now overrides only PYTHONHASHSEED on top
of the inherited environment.

Also folds mint_entity_iri/mint_relationship_iri's hand-rolled
hashlib.sha256(...).hexdigest() into the existing hash_data() helper this
file already imports alongside.

229 export and ontology tests pass, including a new regression test for
the RDF/XML default-type fix.

Co-Authored-By: fabio-rovai <fabio@thetesseractacademy.com>

MANIFEST.in

@@ -1 +1,2 @@
 recursive-include semantica/static *
+recursive-include semantica/ontology/vocabulary *.ttl