Add TRANSFER transaction type with bulk action and auto-rules

- Add TRANSFER to TransactionType enum; excluded from cash flow queries
- Add TransferRule model: description patterns that auto-mark transactions
  as transfers on upload (takes priority over budget rules)
- Bulk action "Mark as transfer" in transaction table
- Transfer Rules button/dialog on transactions page for managing patterns
- Transfers shown with ⇄ prefix and muted color in transaction list

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

prisma/schema.prisma

@@ -13,9 +13,10 @@ model User {
   passwordHash String
   createdAt    DateTime     @default(now())
   updatedAt    DateTime     @updatedAt
-  accounts     Account[]
-  budgets      Budget[]
-  budgetRules  BudgetRule[]
+  accounts      Account[]
+  budgets       Budget[]
+  budgetRules   BudgetRule[]
+  transferRules TransferRule[]
 }
 
 enum AccountType {
@@ -45,6 +46,7 @@ model Account {
 enum TransactionType {
   DEBIT
   CREDIT
+  TRANSFER
 }
 
 model Transaction {
@@ -100,6 +102,16 @@ model BudgetRule {
   @@index([budgetId])
 }
 
+model TransferRule {
+  id        String   @id @default(cuid())
+  userId    String
+  user      User     @relation(fields: [userId], references: [id], onDelete: Cascade)
+  pattern   String
+  createdAt DateTime @default(now())
+
+  @@index([userId])
+}
+
 model CsvUpload {
   id            String        @id @default(cuid())
   accountId     String