Add unit tests for AlertHistory.query() filter combinations

[jason-h23]

Summary

AlertHistory in src/sentinel/history.rs has filtering methods but no test coverage for the query() method, especially for filter combinations and pagination edge cases.

What To Do

Add ~15-20 unit tests covering:

1. Single filters: priority alone, block range alone, pattern type alone
2. Combined filters: all three filters at once
3. Pagination: correct items per page, page boundaries, page > total_pages, page_size clamping (>100)
4. Edge cases: empty file, invalid JSON lines, zero matching alerts
5. Sort order: verify Newest vs Oldest ordering

Files

• src/sentinel/history.rs (add tests at bottom)

Acceptance Criteria

• 15+ test cases covering the scenarios above
• All tests pass (cargo test --all-features)
• No changes to production code (test-only PR)
• Clippy passes

Estimated Effort

~150-200 lines of test code, 2-3 hours