DET-001/002/003: Add IGuidProvider abstraction and refactor Policy.Unknowns for determinism
- Created IGuidProvider interface and SystemGuidProvider in StellaOps.Determinism.Abstractions
- Added SequentialGuidProvider for testing deterministic GUID generation
- Added DeterminismServiceCollectionExtensions with AddDeterminismDefaults()
- Refactored Policy.Unknowns:
- UnknownsRepository now uses TimeProvider and IGuidProvider
- BudgetExceededEventFactory accepts optional TimeProvider parameter
- ServiceCollectionExtensions calls AddDeterminismDefaults()
- Fixed Policy.Exceptions csproj (added ImplicitUsings, Nullable, PackageReferences)
Sprint: SPRINT_20260104_001_BE_determinism_timeprovider_injection
Tasks: DET-001 (audit), DET-002 (IGuidProvider), DET-003 (registration pattern), DET-004 (partial - Policy.Unknowns)