Seeds 120 UPLOADED docs with a deterministic date spread and runs
DocumentService.searchDocuments against a Testcontainers Postgres, not
a Mockito mock. Five cases:
1. First page returns exactly page_size items + correct totalElements
2. Last partial page returns the tail slice (offset 100 → 20 items)
3. Page beyond last returns empty content, totalElements still 120
4. SENDER sort path slices in-memory + reports correct total
5. Different pages return disjoint document id sets
Closes the integration-coverage gap between the Mockito unit tests and
the full Spec→Pageable→Page→DTO path that unit tests can't exercise.
Runs in ~87 s against the shared Testcontainers instance. (#316)
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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