Reinstate QueryDocumentsAsync SQL implementation

[Copilot]

Description

The QueryDocumentsAsync method in SqlitePeerStore was replaced with a placeholder returning empty results, breaking PeerCollection.Find and query-based APIs.

Restored the complete SQL-based query implementation with:

• Query expression translation via SqlQueryTranslator
• Paging support (LIMIT/OFFSET for skip/take parameters)
• Collection filtering for both per-collection and legacy table modes
• Field ordering with json_extract for custom fields, defaulting to Key
• Proper type conversion for IsDeleted field (int → bool)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• QueryDocumentsAsync_ShouldSupportPaging test validates paging functionality
• All 26 persistence layer tests pass
• CodeQL security scan shows no vulnerabilities

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

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