Add Myspace retrieval ranking evaluation fixtures

[SahilKumar75]

Summary

Create evaluation fixtures for Myspace retrieval so ranking changes can be tested against realistic saved notes, screenshots, tags, and OCR text.

Scope

• Add fixture data with saved Myspace items and search queries.
• Define expected top results and match explanations.
• Cover subject aliases, OCR text, tags, and recent search suggestions.
• Keep the fixture deterministic and small enough for CI.

Acceptance Criteria

• A test or script can evaluate Myspace retrieval ranking against fixtures.
• Expected matches include explanation labels.
• The fixture covers at least one OCR-heavy saved screenshot case.
• The PR documents how to run the evaluation.