Phase 1-4: Add soft delete, concurrency token, update EF config and controllers

- Add ISoftDeletable interface with IsDeleted/DeletedAt
- Implement on Budget, Income, Outgo, BudgetShare; add RowVersion (xmin) to Budget
- Configure EF global query filters and xmin concurrency token
- Replace Remove() with soft delete in all delete endpoints
- Wrap Budget.Update SaveChanges in DbUpdateConcurrencyException catch

src/Budget.Infrastructure/Data/AppDbContext.cs

@@ -22,6 +22,12 @@ public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(op
             b.HasMany(x => x.Incomes).WithOne(i => i.Budget).HasForeignKey(i => i.BudgetId).OnDelete(DeleteBehavior.Cascade);
             b.HasMany(x => x.Outgos).WithOne(o => o.Budget).HasForeignKey(o => o.BudgetId).OnDelete(DeleteBehavior.Cascade);
             b.HasMany(x => x.Shares).WithOne(s => s.Budget).HasForeignKey(s => s.BudgetId).OnDelete(DeleteBehavior.Cascade);
+            b.HasQueryFilter(x => !x.IsDeleted);
+            b.Property(e => e.RowVersion)
+                .HasColumnName("xmin")
+                .HasColumnType("xid")
+                .ValueGeneratedOnAddOrUpdate()
+                .IsConcurrencyToken();
         });
 
         modelBuilder.Entity<Income>(b =>
@@ -29,6 +35,7 @@ public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(op
             b.HasKey(x => x.Id);
             b.Property(x => x.Name).IsRequired().HasMaxLength(200);
             b.Property(x => x.Amount).HasPrecision(18, 2);
+            b.HasQueryFilter(x => !x.IsDeleted);
         });
 
         modelBuilder.Entity<Outgo>(b =>
@@ -39,6 +46,7 @@ public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(op
             b.Property(x => x.PaymentSource).HasMaxLength(100);
             b.Property(x => x.Notes).HasMaxLength(1000);
             b.Property(x => x.Amount).HasPrecision(18, 2);
+            b.HasQueryFilter(x => !x.IsDeleted);
         });
 
         modelBuilder.Entity<KnownUser>(b =>
@@ -55,6 +63,7 @@ public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(op
             b.Property(x => x.SharedWithUserId).HasMaxLength(200);
             b.Property(x => x.SharedWithEmail).IsRequired().HasMaxLength(200);
             b.HasIndex(x => new { x.BudgetId, x.SharedWithEmail }).IsUnique();
+            b.HasQueryFilter(x => !x.IsDeleted);
         });
     }
 }