P0: Harden deterministic document chunking contract

[sfloess]

Summary

• make implicit document IDs deterministic
• preserve requested overlap when splitting oversized segments without redundant final windows
• recognize ., !, and ? sentence boundaries
• add Unicode, metadata, provenance, offset, determinism, and overlap tests
• verify the scraping AcquiredResource contract through a fixture without coupling imports
• adopt the FlossWare X.Y version convention (0.1)
• add minimal GitHub Actions test coverage

Validation

The branch contains the P0 acceptance coverage. Local execution is unavailable in this environment because outbound GitHub/DNS access is unavailable; CI should be the authoritative test run.

Review

Please review against the P0 acceptance criteria, especially deterministic behavior, provenance/offset correctness, overlap semantics, and the scraping -> document contract <- chunking boundary.

Do not merge until reviewed.

[sonarqubecloud]

Quality Gate failed

Failed conditions
C Security Rating on New Code (required ≥ A)

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