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/SchedulerJobBase.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace QuantEngine.Core.Scheduling
+{
+    /// <summary>
+    /// Base class for all scheduled jobs.
+    ///
+    /// Responsibilities:
+    /// - Implement consistent lifecycle (Start → Run → End)
+    /// - Log execution metrics
+    /// - Handle errors gracefully
+    /// - Record success/failure for monitoring
+    /// </summary>
+    public abstract class SchedulerJobBase
+    {
+        public string JobId { get; protected set; } = string.Empty;
+        public string Description { get; protected set; } = string.Empty;
+        public DateTime? LastRun { get; private set; }
+
+        /// <summary>
+        /// Execute the job with complete lifecycle.
+        /// </summary>
+        public async Task ExecuteAsync()
+        {
+            var startTime = DateTime.UtcNow;
+            try
+            {
+                Console.WriteLine($"[{JobId}] Started: {Description}");
+                await RunAsync();
+                Console.WriteLine($"[{JobId}] Completed in {(DateTime.UtcNow - startTime).TotalSeconds:F2}s");
+                LastRun = startTime;
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine($"[{JobId}] Failed: {ex.Message}");
+                throw;
+            }
+        }
+
+        /// <summary>
+        /// Override this method to implement the actual job logic.
+        /// </summary>
+        protected abstract Task RunAsync();
+    }
+}