feat: disable identity auto-generation for reference/lookup tables

Reference tables (Province, City, BasicTable, IncomeCostTitle, UnitState, Transaction) require stable, manually assigned IDs that are cross-referenced by other entities. Identity auto-generation is disabled to allow explicit ID assignment from seed data.

Complex.Infrastructure/ComplexDBContext.cs

@@ -77,6 +77,43 @@ namespace Complex.Infrastructure
                 .WithMany()
                 .HasForeignKey(uc => uc.UnitId)
                 .OnDelete(DeleteBehavior.NoAction);
+
+            // ============================================================
+            // Reference/Lookup tables: These have fixed, meaningful IDs
+            // that are explicitly set in seed data and cross-referenced
+            // by other entities. Identity auto-generation must be disabled.
+            // ============================================================
+
+            // Province: ProvinceId (1-31) are stable identifiers
+            builder.Entity<Province>()
+                .Property(p => p.ProvinceId)
+                .ValueGeneratedNever();
+
+            // City: CityId (101, 102, ...) are meaningful (provinceId * 100 + index)
+            builder.Entity<City>()
+                .Property(c => c.CityId)
+                .ValueGeneratedNever();
+
+            // BasicTable (base for TransactionType): Id (1,2) are fixed reference data
+            builder.Entity<BasicTable>()
+                .Property(b => b.Id)
+                .ValueGeneratedNever();
+
+            // IncomeCostTitle: Id (1-12) are fixed reference data
+            builder.Entity<IncomeCostTitle>()
+                .Property(i => i.Id)
+                .ValueGeneratedNever();
+
+            // UnitState: Id (1-5) are fixed reference data
+            builder.Entity<UnitState>()
+                .Property(u => u.Id)
+                .ValueGeneratedNever();
+
+            // Transaction: Seeder uses explicit IDs (1,2,3) that are
+            // cross-referenced by UnitCost.TransactionId
+            builder.Entity<Transaction>()
+                .Property(t => t.Id)
+                .ValueGeneratedNever();
         }