Adds TestOPDSSearchAcrossLibraries function to verify that OPDS
search endpoint works across multiple libraries. Test creates:
1. Two separate libraries with unique IDs
2. Books in each library (OPDS Book 1, OPDS Book 2)
3. Test device for OPDS authentication
4. Searches without library_id parameter
Test validates that:
- OPDS returns 200 (not 404)
- Response contains both books from different libraries
- Cross-library search functionality works as expected
This test served as verification that the SQL NULL handling pattern
used by OPDS (2-part check) works correctly for cross-library searches.
john-okeefe
7ecfbcdb73