Normalize all DateTime values to UTC across the codebase

Npgsql requires DateTimeKind.Utc for timestamp with time zone
columns. This fixes errors in transaction create/edit, budgets,
reports, loans, scheduled transactions, and file imports.

Changes:
- TransactionService: SpecifyKind on request.Date for create,
  update, and transfer
- BudgetService: UTC kind on all new DateTime(year, month, 1)
- ReportService: UTC kind on endOfMonth; rewrite spending-by-
  category GroupBy to avoid untranslatable navigation properties
- LoanService: UTC kind on payoff scenario date construction
- ScheduledTransactionService: UTC kind on SemiMonthly date
- ImportService: SpecifyKind on parsed.Date when persisting
- OFX/CSV/QIF parsers: AssumeUniversal + AdjustToUniversal on
  all date parsing

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

src/Purrse.Api/Services/BudgetService.cs

@@ -21,7 +21,7 @@ public class BudgetService : IBudgetService
 
         if (budget == null) return null;
 
-        var startDate = new DateTime(year, month, 1);
+        var startDate = new DateTime(year, month, 1, 0, 0, 0, DateTimeKind.Utc);
         var endDate = startDate.AddMonths(1).AddDays(-1);
         var actuals = await GetActualSpending(userId, startDate, endDate);
 
@@ -77,7 +77,7 @@ public class BudgetService : IBudgetService
 
         await _db.SaveChangesAsync();
 
-        var startDate = new DateTime(budget.Year, budget.Month, 1);
+        var startDate = new DateTime(budget.Year, budget.Month, 1, 0, 0, 0, DateTimeKind.Utc);
         var endDate = startDate.AddMonths(1).AddDays(-1);
         var actuals = await GetActualSpending(userId, startDate, endDate);
 
@@ -98,7 +98,7 @@ public class BudgetService : IBudgetService
             .FirstOrDefaultAsync(b => b.Id == budgetId && b.UserId == userId)
             ?? throw new KeyNotFoundException("Budget not found");
 
-        var startDate = new DateTime(budget.Year, budget.Month, 1);
+        var startDate = new DateTime(budget.Year, budget.Month, 1, 0, 0, 0, DateTimeKind.Utc);
         var endDate = startDate.AddMonths(1).AddDays(-1);
         var actuals = await GetActualSpending(userId, startDate, endDate);
 

src/Purrse.Api/Services/ImportService.cs

@@ -215,7 +215,7 @@ public class ImportService : IImportService
         {
             Id = Guid.NewGuid(),
             AccountId = batch.AccountId,
-            Date = parsed.Date,
+            Date = DateTime.SpecifyKind(parsed.Date, DateTimeKind.Utc),
             Amount = parsed.Amount,
             PayeeId = matchedPayee?.Id,
             PayeeName = parsed.PayeeName,

src/Purrse.Api/Services/LoanService.cs

@@ -115,8 +115,8 @@ public class LoanService : ILoanService
         var monthlyRate = l.InterestRate / 100 / 12;
         var extraMonthly = request.ExtraMonthlyPayment ?? 0;
         var basePayment = l.MonthlyPayment - (l.EscrowAmount ?? 0);
-        var paymentDate = DateTime.UtcNow.Date;
-        paymentDate = new DateTime(paymentDate.Year, paymentDate.Month, l.OriginationDate.Day);
+        var now = DateTime.UtcNow;
+        var paymentDate = new DateTime(now.Year, now.Month, l.OriginationDate.Day, 0, 0, 0, DateTimeKind.Utc);
 
         var newEntries = new List<AmortizationEntryResponse>();
         int paymentNum = 0;

src/Purrse.Api/Services/ReportService.cs

@@ -23,15 +23,24 @@ public class ReportService : IReportService
             query = query.Where(t => t.AccountId == accountId.Value);
 
         var groups = await query
-            .GroupBy(t => new { t.CategoryId, CategoryName = t.Category!.Name, ParentName = t.Category.Parent != null ? t.Category.Parent.Name : (string?)null })
-            .Select(g => new { g.Key.CategoryName, g.Key.ParentName, Amount = Math.Abs(g.Sum(t => t.Amount)) })
+            .GroupBy(t => t.CategoryId)
+            .Select(g => new { CategoryId = g.Key, Amount = -g.Sum(t => t.Amount) })
             .OrderByDescending(g => g.Amount)
             .ToListAsync();
 
+        var categoryIds = groups.Select(g => g.CategoryId).ToList();
+        var categoryLookup = await _db.Categories
+            .Include(c => c.Parent)
+            .Where(c => categoryIds.Contains(c.Id))
+            .ToDictionaryAsync(c => c.Id, c => new { c.Name, ParentName = c.Parent != null ? c.Parent.Name : (string?)null });
+
         var total = groups.Sum(g => g.Amount);
-        var categories = groups.Select(g => new CategorySpending(
-            g.CategoryName, g.Amount, total > 0 ? (g.Amount / total) * 100 : 0, g.ParentName
-        )).ToList();
+        var categories = groups.Select(g =>
+        {
+            var cat = categoryLookup.GetValueOrDefault(g.CategoryId!.Value);
+            return new CategorySpending(
+                cat?.Name ?? "Unknown", g.Amount, total > 0 ? (g.Amount / total) * 100 : 0, cat?.ParentName);
+        }).ToList();
 
         return new SpendingByCategoryReport(startDate, endDate, total, categories);
     }
@@ -71,7 +80,7 @@ public class ReportService : IReportService
 
         while (currentDate <= endDate)
         {
-            var endOfMonth = new DateTime(currentDate.Year, currentDate.Month, DateTime.DaysInMonth(currentDate.Year, currentDate.Month));
+            var endOfMonth = new DateTime(currentDate.Year, currentDate.Month, DateTime.DaysInMonth(currentDate.Year, currentDate.Month), 0, 0, 0, DateTimeKind.Utc);
             var txnsToDate = transactions.Where(t => t.Date <= endOfMonth).Sum(t => t.Amount);
 
             // Simplified: using current balances adjusted by future transactions

src/Purrse.Api/Services/ScheduledTransactionService.cs

@@ -141,7 +141,7 @@ public class ScheduledTransactionService : IScheduledTransactionService
         Frequency.Daily => current.AddDays(1),
         Frequency.Weekly => current.AddDays(7),
         Frequency.BiWeekly => current.AddDays(14),
-        Frequency.SemiMonthly => current.Day <= 15 ? new DateTime(current.Year, current.Month, Math.Min(28, DateTime.DaysInMonth(current.Year, current.Month))) : current.AddMonths(1).AddDays(-(current.Day - 1)),
+        Frequency.SemiMonthly => current.Day <= 15 ? new DateTime(current.Year, current.Month, Math.Min(28, DateTime.DaysInMonth(current.Year, current.Month)), 0, 0, 0, DateTimeKind.Utc) : current.AddMonths(1).AddDays(-(current.Day - 1)),
         Frequency.Monthly => current.AddMonths(1),
         Frequency.Quarterly => current.AddMonths(3),
         Frequency.SemiAnnually => current.AddMonths(6),

src/Purrse.Api/Services/TransactionService.cs

@@ -47,7 +47,7 @@ public class TransactionService : ITransactionService
         {
             Id = Guid.NewGuid(),
             AccountId = request.AccountId,
-            Date = request.Date,
+            Date = DateTime.SpecifyKind(request.Date, DateTimeKind.Utc),
             Amount = request.Amount,
             PayeeName = request.PayeeName,
             PayeeId = request.PayeeId,
@@ -89,7 +89,7 @@ public class TransactionService : ITransactionService
             ?? throw new KeyNotFoundException("Transaction not found");
 
         var oldAmount = transaction.Amount;
-        transaction.Date = request.Date;
+        transaction.Date = DateTime.SpecifyKind(request.Date, DateTimeKind.Utc);
         transaction.Amount = request.Amount;
         transaction.PayeeName = request.PayeeName;
         transaction.PayeeId = request.PayeeId;
@@ -181,7 +181,7 @@ public class TransactionService : ITransactionService
         {
             Id = Guid.NewGuid(),
             AccountId = request.FromAccountId,
-            Date = request.Date,
+            Date = DateTime.SpecifyKind(request.Date, DateTimeKind.Utc),
             Amount = -Math.Abs(request.Amount),
             PayeeName = $"Transfer to {toAccount.Name}",
             Memo = request.Memo,
@@ -193,7 +193,7 @@ public class TransactionService : ITransactionService
         {
             Id = Guid.NewGuid(),
             AccountId = request.ToAccountId,
-            Date = request.Date,
+            Date = DateTime.SpecifyKind(request.Date, DateTimeKind.Utc),
             Amount = Math.Abs(request.Amount),
             PayeeName = $"Transfer from {fromAccount.Name}",
             Memo = request.Memo,