feat: add admin authentication and management features

- Implemented Prisma schema with models for AdminUser, AppSettings, and Snapshot.
- Created seed script to initialize the database with an admin user and JWT secret.
- Developed admin login page with form handling and error management.
- Added API routes for admin login, logout, change password, and JWT verification.
- Integrated Stripe for payment intent management in admin orders.
- Established middleware for protecting admin routes with JWT authentication.
- Created Zustand stores for managing persona and snapshot states.

prisma/schema.prisma

@@ -0,0 +1,28 @@
+generator client {
+  provider = "prisma-client"
+  output   = "../src/generated/prisma"
+}
+
+datasource db {
+  provider = "sqlite"
+}
+
+model AdminUser {
+  id           String   @id @default(cuid())
+  username     String   @unique
+  passwordHash String
+  createdAt    DateTime @default(now())
+  updatedAt    DateTime @updatedAt
+}
+
+model AppSettings {
+  key       String   @id
+  value     String
+  updatedAt DateTime @updatedAt
+}
+
+model Snapshot {
+  paymentIntentId String   @id
+  imageData       String
+  createdAt       DateTime @default(now())
+}