v0.5.0

Initial public MaxVol checkpoint.\n\nSummary:\n- Adds dense column-major matrix storage and public result/error/options types.\n- Implements square MaxVol for Double with modern Accelerate LAPACK/CBLAS headers.\n- Aligns tolerance and iteration-limit behavior with maxvolpy reference fixtures while exposing convergence status.\n- Adds Swift Testing coverage, DocC, SPI metadata, and v1 roadmap planning.\n\nVerification:\n- swift build\n- swift test\n- swift package dump-package\n- xcrun docc convert\n- scripts/repo-maintenance/validate-all.sh\n- GitHub Actions validate workflow