feat: category import from CSV + budget auto-assign rules

Category:
- Add categoryColumn to NormalizerConfig and NormalizedRow
- Map 'Category' column for Discover CC profile
- Write category to Transaction on upload

Budget rules:
- Add BudgetRule model (userId, budgetId, pattern)
- API: GET/POST /api/budget-rules, DELETE /api/budget-rules/:id
- Apply rules during upload (first case-insensitive match wins)
- Budgets page fetches and passes rules per budget
- BudgetCard 'Rules' menu item opens BudgetRulesDialog for add/delete

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

prisma/schema.prisma

@@ -8,13 +8,14 @@ datasource db {
 }
 
 model User {
-  id           String    @id @default(cuid())
-  email        String    @unique
+  id           String       @id @default(cuid())
+  email        String       @unique
   passwordHash String
-  createdAt    DateTime  @default(now())
-  updatedAt    DateTime  @updatedAt
+  createdAt    DateTime     @default(now())
+  updatedAt    DateTime     @updatedAt
   accounts     Account[]
   budgets      Budget[]
+  budgetRules  BudgetRule[]
 }
 
 enum AccountType {
@@ -80,10 +81,24 @@ model Budget {
   createdAt    DateTime      @default(now())
   updatedAt    DateTime      @updatedAt
   transactions Transaction[]
+  rules        BudgetRule[]
 
   @@index([userId])
 }
 
+model BudgetRule {
+  id        String   @id @default(cuid())
+  userId    String
+  user      User     @relation(fields: [userId], references: [id], onDelete: Cascade)
+  budgetId  String
+  budget    Budget   @relation(fields: [budgetId], references: [id], onDelete: Cascade)
+  pattern   String
+  createdAt DateTime @default(now())
+
+  @@index([userId])
+  @@index([budgetId])
+}
+
 model CsvUpload {
   id            String        @id @default(cuid())
   accountId     String