build(verification): local build success + migrations validated

Build Results:
✓ .NET Release build: 0 errors, 0 warnings
✓ Core unit tests: 214/214 passed
✓ Migration files: 607 lines total
  - V003 (audit trail): 319 lines (3 tables, 3 views)
  - V004 (3NF normalization): 288 lines (4 tables, 9 indexes, 2 views)

New Files:
✓ SchedulerJobBase.cs - Base class for scheduled jobs
✓ IDataValidator.cs - Validation interface
✓ ISnapshotRepository.cs - Repository pattern interface
✓ V003_add_audit_trail_tables.sql - Audit infrastructure
✓ V004_normalize_snapshots_schema.sql - 3NF schema migration

Status: Phase 0-1 infrastructure ready for deployment

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/dotnet/QuantEngine.Core/Scheduling/IDataValidator.cs

@@ -0,0 +1,27 @@
+using System.Collections.Generic;
+
+namespace QuantEngine.Core.Scheduling
+{
+    /// <summary>
+    /// Data validation interface for quality gates.
+    /// Part of Phase 0: 5-point validation (Completeness, Freshness, Consistency, Outliers, Duplicates).
+    /// </summary>
+    public interface IDataValidator
+    {
+        /// <summary>
+        /// Validate a single snapshot record.
+        /// Returns result with status and failed checks.
+        /// </summary>
+        ValidationResult Validate(Dictionary<string, object> data);
+    }
+
+    /// <summary>
+    /// Validation result with detailed failure information.
+    /// </summary>
+    public class ValidationResult
+    {
+        public bool IsValid { get; set; }
+        public List<string> FailedChecks { get; set; } = new();
+        public string Status { get; set; } = "PASS";
+    }
+}