Promote Nexus Unity 1.4.1 release docs to main

[Daliys]

Summary

• Promotes the finalized Nexus Unity 1.4.1 release documentation from development to main.
• Updates remaining release/version examples from 1.4.0 / v1.4.0 to 1.4.1 / v1.4.1.
• Aligns the 1.4.1 changelog date with the actual June 12, 2026 release flow.

Branch audit

• feat/claude-code-integration is already fully merged into both development and main.
• fix/missing-folder-metas is already fully merged into both development and main.
• No extra branch content needs to be included in 1.4.1.

Validation

• python3 -m unittest discover -s Editor/tests -v passed locally.
• bash scripts/prepush-validate.sh --static-only passed locally.
• bash scripts/prepush-validate.sh --quick passed locally.
• PR Finalize Nexus Unity 1.4.1 release docs #41 checks passed before merging into development: PR target policy, Static validation, Python unit tests, Documentation quality AI, Unity package smoke.