Fix reorder: normalize SortOrder after move, remove AsNoTracking from write path

The shift-in-place approach broke when SortOrder values had gaps from soft
deletes. Switch to remove/insert then assign SortOrder = index, which is
correct regardless of initial values. Also fix OutgosController Reorder
which had AsNoTracking applied from the M-3 change, silently dropping saves.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Budget.Api/Controllers/IncomesController.cs

@@ -105,11 +105,10 @@ public class IncomesController(AppDbContext db, BudgetAuthorizationService authz
         var oldIdx = incomes.IndexOf(item);
         var newIdx = Math.Clamp(req.NewIndex, 0, incomes.Count - 1);
         if (oldIdx == newIdx) return NoContent();
-        if (newIdx < oldIdx)
-            for (int i = newIdx; i < oldIdx; i++) incomes[i].SortOrder++;
-        else
-            for (int i = oldIdx + 1; i <= newIdx; i++) incomes[i].SortOrder--;
-        item.SortOrder = newIdx;
+        incomes.RemoveAt(oldIdx);
+        incomes.Insert(newIdx, item);
+        for (int i = 0; i < incomes.Count; i++)
+            incomes[i].SortOrder = i;
         await db.SaveChangesAsync();
         return NoContent();
     }

src/Budget.Api/Controllers/OutgosController.cs

@@ -116,17 +116,16 @@ public class OutgosController(AppDbContext db, BudgetAuthorizationService authz)
     {
         if (TryGetUserId(out var userId) is { } err) return err;
         if (!await authz.CanWriteAsync(budgetId, userId)) return Forbid();
-        var outgos = await db.Outgos.AsNoTracking().Where(o => o.BudgetId == budgetId).OrderBy(o => o.SortOrder).ToListAsync();
+        var outgos = await db.Outgos.Where(o => o.BudgetId == budgetId).OrderBy(o => o.SortOrder).ToListAsync();
         var item = outgos.FirstOrDefault(o => o.Id == req.Id);
         if (item is null) return NotFound();
         var oldIdx = outgos.IndexOf(item);
         var newIdx = Math.Clamp(req.NewIndex, 0, outgos.Count - 1);
         if (oldIdx == newIdx) return NoContent();
-        if (newIdx < oldIdx)
-            for (int i = newIdx; i < oldIdx; i++) outgos[i].SortOrder++;
-        else
-            for (int i = oldIdx + 1; i <= newIdx; i++) outgos[i].SortOrder--;
-        item.SortOrder = newIdx;
+        outgos.RemoveAt(oldIdx);
+        outgos.Insert(newIdx, item);
+        for (int i = 0; i < outgos.Count; i++)
+            outgos[i].SortOrder = i;
         await db.SaveChangesAsync();
         return NoContent();
     }