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>

src/app/api/budget-rules/route.ts

@@ -0,0 +1,37 @@
+import { NextResponse } from 'next/server'
+import { auth } from '@/lib/auth'
+import { prisma } from '@/lib/prisma'
+import { createBudgetRuleSchema } from '@/lib/validations/budget-rule'
+
+export async function GET() {
+  const session = await auth()
+  if (!session?.user?.id) return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+
+  const rules = await prisma.budgetRule.findMany({
+    where: { userId: session.user.id },
+    orderBy: { createdAt: 'asc' },
+    select: { id: true, budgetId: true, pattern: true },
+  })
+  return NextResponse.json(rules)
+}
+
+export async function POST(req: Request) {
+  const session = await auth()
+  if (!session?.user?.id) return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+
+  const body = await req.json()
+  const parsed = createBudgetRuleSchema.safeParse(body)
+  if (!parsed.success) return NextResponse.json({ error: parsed.error.flatten() }, { status: 400 })
+
+  const { budgetId, pattern } = parsed.data
+
+  // Verify budget belongs to this user
+  const budget = await prisma.budget.findFirst({ where: { id: budgetId, userId: session.user.id } })
+  if (!budget) return NextResponse.json({ error: 'Budget not found' }, { status: 404 })
+
+  const rule = await prisma.budgetRule.create({
+    data: { userId: session.user.id, budgetId, pattern },
+    select: { id: true, budgetId: true, pattern: true },
+  })
+  return NextResponse.json(rule, { status: 201 })
+}