Add offline monthly insights with Ollama

prisma/migrations/20260323133000_add_monthly_insight_unique/migration.sql

@@ -0,0 +1,3 @@
+-- CreateIndex
+CREATE UNIQUE INDEX "MonthlyInsight_month_key" ON "MonthlyInsight"("month");
+

prisma/schema.prisma

@@ -36,7 +36,7 @@ model Paycheck {
 
 model MonthlyInsight {
   id              String   @id @default(cuid())
-  month           String
+  month           String   @unique
   year            Int
   generatedAt     DateTime @default(now())
   summary         String