feat: add NotesMixin to Contact model for enhanced note functionality

[jirhiker]

Why

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How

Implementation summary - the following was changed / added / removed:

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Notes

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[Copilot]

Pull request overview

This PR adds the NotesMixin to the Contact model to provide note-taking functionality for contact records.

Changes:

• Import NotesMixin from the db module
• Add NotesMixin as a parent class to the Contact model

[chatgpt-codex-connector]

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