Resolve data persistence & query compilation - ready for performance phase

- QueryCompiler: Fixed WHERE clause type handling (IComparable, numeric coercion)
- Database: Confirmed InsertBatch() working (141/200 mystery SOLVED, 200/200 persisting)
- Tests: All CompiledQueryTests passing, 1000 queries complete in 137-1466ms
- Status: Stable checkpoint before performance optimization phase
- Next: Focus on eliminating thread sleeps for flush operations"

Author: MPCoreDeveloper

src/SharpCoreDB/Services/QueryCompiler.cs

@@ -260,9 +260,11 @@ private static Expression CompareUsingIComparable(Expression left, Expression ri
             left = Expression.Convert(left, typeof(IComparable));
         }
 
-        if (right.Type == typeof(object))
+        // ✅ FIX: Always convert right to object for CompareTo parameter
+        // CompareTo expects object, not specific types like int
+        if (right.Type != typeof(object))
         {
-            right = Expression.Convert(right, typeof(object)); // Keep as object for CompareTo parameter
+            right = Expression.Convert(right, typeof(object));
         }
 
         // Call: left.CompareTo(right)