Code quality: fix all ruff warnings, add CI/CD, improve test coverage

Sprint 10: ViewerProjection builder — overlay generation and inspection

Sprint 9: complete provider system — runtimes, adapters, registry, resolver

Sprint 7: persistence layer and job orchestration

Sprint 6: enricher subsystem — 6 enrichers with pipeline and policy control

Sprint 5: PAGE XML serializer and dual export

Sprint 4: validation layer and document policy

Sprint 3: vertical slice — PaddleOCR adapter, normalization pipeline, ALTO serializer

Sprint 2: geometry subsystem — operations, transforms, normalization, quantization

Sprint 1: complete domain models — canonical document, geometry, provenance, readiness

Sprint 0: project foundation — structure, settings, FastAPI skeleton