fix(vector): align MESA_Data evidence with V4 vector contract

[Yasou13]

Summary

• cap publisher chunks at the MESA V4 4,096-character evidence-span limit
• publish the full chunk as evidence_span and reject oversized manual payloads
• add real SQLite/LanceDB/Kùzu cross-repository compatibility coverage

Verification

• 395 passed, 1 skipped, 4 deselected (non-scale)
• 4 passed (scale)
• 37 passed (focused MESA vector/embedding/rebuild tests)
• cross-repository real-store compatibility: 1 passed
• Ruff and compileall passed

Notes

• Repository-wide format, mypy, and security baselines still have unrelated pre-existing issues documented during validation.

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