[WIP] Implement lookup-before-insert behavior for reference rows

[Codex]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

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This section details on the original issue you should resolve

<issue_title>Prevent duplicate inserts for canonical/reference rows</issue_title>
<issue_description>## Summary
Implement lookup-before-insert behavior for canonical/reference entities that should be reused instead of duplicated.

Scope

• Identify reference-row creation paths
• Add lookup-and-reuse behavior before insert
• Align normalization/comparison with database uniqueness semantics

Deliverables

• Repository/service support for reuse instead of duplicate creation
• Tests covering existing-row reuse behavior

Acceptance criteria

• Existing canonical rows are reused when equivalent input is provided
• Covered paths no longer attempt duplicate inserts
• Behavior remains client-transparent where appropriate

Testing

• Unit tests for lookup-before-insert behavior
• Integration tests proving existing canonical rows are reused

Dependencies

• Depends on the duplicate-handling policy sub-issue

Parent: #887</issue_description>

Comments on the Issue (you are @codex[agent] in this section)

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud