test(build): add no-poi Maven profile to validate poi-ooxml stays optional (I1)

[DemchaAV]

Summary

Wires up Track I1 from the v1.6.5→1.7 readiness taskboard. poi-ooxml is declared <optional>true</optional> in pom.xml so callers that render only PDFs don't pay the ~10 MB POI footprint; this PR ships the regression gate that proves the rest of the canonical suite runs without it.

What changes

no-poi profile in pom.xml

$ ./mvnw -P no-poi test -pl .

Activates a profile that does two things via maven-surefire-plugin:

• Excludes POI from the test classpath via <classpathDependencyExcludes>: org.apache.poi:poi-ooxml, org.apache.poi:poi, org.apache.poi:poi-ooxml-lite. No POI on the classpath at test runtime — any unconditional reference becomes NoClassDefFoundError.
• Sets no.poi=true system property so DOCX-specific tests can self-skip.

Two tests carry @DisabledIfSystemProperty(named = "no.poi", matches = "true")

Test	Why
DocxSemanticBackendTest (whole class)	Every test imports org.apache.poi.xwpf.usermodel.* and exercises DocxSemanticBackend end-to-end.
DocumentSessionTest#semanticBackendsShouldExportManifestsFromDocumentGraph	Single test that asserts session.export(new DocxSemanticBackend()) produces a ZIP-shaped DOCX byte stream.

Both skip cleanly under -P no-poi. All other tests — including the rest of DocumentSessionTest — run green without POI on the classpath.

New CI job — no-poi-suite

PR-only, runs after the architecture guards job, executes ./mvnw -B -ntp test -pl . -P no-poi. Adds the regression gate to every PR so a future change that quietly introduces an unconditional POI reference fails the job rather than silently re-coupling the optional dependency.

Verification

$ ./mvnw -B -ntp test -pl . -P no-poi
Tests run: 1029, Failures: 0, Errors: 0, Skipped: 4
BUILD SUCCESS (~65s)

4 skipped == DocxSemanticBackendTest (3 tests) + 1 method in DocumentSessionTest — exactly the methods I annotated. The other 1025 tests ran without POI on the classpath, validating the <optional> declaration.

CHANGELOG entry added to v1.6.6 — Planned under the ### Build subsection.

Why this scope

• Profile-level exclusion, not pom-level removal — poi-ooxml stays a declared dependency so consumers that do need DOCX still resolve it transitively; the profile is for us to test the no-POI footprint.
• Skip annotation, not test removal — the DOCX backend is still production code under active use; the tests stay green by default and only skip when the profile says "validate without POI".
• No production-code changes — DocxSemanticBackend.java itself is untouched. The taskboard says "DOCX backend disabled gracefully"; gracefully here means "the suite around it doesn't fall over when POI is absent", which is what this validates.

Test plan

• -P no-poi profile green locally (1029 / 0 / 0 / 4 skipped)
• Default suite (no profile) still green
• binary-compat profile unchanged (still in the same <profiles> block)
• CI green on PR, including the new no-poi-suite job
• Reviewer skim — the profile config (15 LOC in pom.xml) and the two @DisabledIfSystemProperty placements are the load-bearing pieces
• (Out of scope) follow-up: a real consumer-side smoke test in a downstream repo that depends on graphcompose without explicitly adding poi-ooxml — tracked as v1.6.6 release-prep checklist item