refactor: migrate database layer to Prisma ORM

prisma/schema.prisma

@@ -0,0 +1,42 @@
+generator client {
+  provider = "prisma-client-js"
+}
+
+datasource db {
+  provider = "sqlite"
+  url      = env("DATABASE_URL")
+}
+
+model User {
+  id        Int      @id @default(autoincrement())
+  username  String   @unique
+  password  String
+  name      String
+  email     String?
+  role      String   @default("user")
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+  serials   Serial[]
+}
+
+model Company {
+  id          Int      @id @default(autoincrement())
+  companyName String   @unique
+  isActive    Boolean  @default(true)
+  createdAt   DateTime @default(now())
+  updatedAt   DateTime @updatedAt
+  serials     Serial[]
+}
+
+model Serial {
+  id          Int      @id @default(autoincrement())
+  serialNumber String  @unique
+  companyName String
+  validUntil  DateTime?
+  isActive    Boolean  @default(true)
+  createdBy   Int?
+  createdAt   DateTime @default(now())
+  updatedAt   DateTime @updatedAt
+  user        User?    @relation(fields: [createdBy], references: [id])
+  company     Company? @relation(fields: [companyName], references: [companyName])
+}