feat(delta): additive schema evolution for append/overwrite + reporting/events

[malon64]

Summary

• enable additive-only Delta schema evolution for append/overwrite when
• keep strict behavior for incompatible changes and merge modes
• emit run event when evolution is applied
• surface block in entity run reports (applied and no-op cases)
• add unit/integration tests and update docs (write modes, delta sink, report)

Validation

• orchestrator lint step (fmt + clippy + relevant Rust tests) passed

[chatgpt-codex-connector]

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