* Serve namespace ontology terms from ProxyRequestFilter

After the DataManager cache check, run a DESCRIBE query against the
app's in-memory OntModel (full imports closure) before falling through
to the external proxy or 405. Covers both slash-based term URIs (e.g.
schema:category) and hash-based namespaces (e.g. sioc:ns → describes
all sioc:ns#* terms via the WHERE clause). This allows facet headers
and other term lookups to resolve from imported ontologies without
requiring ENABLE_LINKED_DATA_PROXY=true.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Add proxy test for OntModel namespace term lookup

Creates two OWL classes in a made-up hash-based namespace, clears
the in-memory ontology, then retrieves the namespace document via
?uri= and verifies both class descriptions are returned. The namespace
is not DataManager-mapped and not a registered app, so the request
exercises the new OntModel DESCRIBE path in ProxyRequestFilter.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Fix ProxyRequestFilterTest after ontology injection added

Set filter.ontology = Optional.empty() in setUp() so existing tests
reach the proxy/NotAllowed paths they were designed to test.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Injection fixes

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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>