Add configurable SearchAlpha parameter for hybrid search tuning
- Added SearchAlpha config parameter (default: 0.7) for tuning BM25 vs vector search balance
- Updated NewWeaviateWrapper to accept host and searchAlpha parameters
- Enhanced hybrid search with configurable alpha parameter via WithAlpha()
- Fixed all type mismatches in mocks and tests to use domainsearch.SearchResults
- Updated GraphQL resolver to use new SearchResults structure with SearchResultItem
- All tests and vet checks passing
Closes#30
