feat: add Prisma schema (MySQL) and Docker Compose for db/redis

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/lib/prisma.ts

@@ -0,0 +1,17 @@
+import { PrismaClient } from "@prisma/client";
+import { PrismaMariaDb } from "@prisma/adapter-mariadb";
+
+const globalForPrisma = globalThis as unknown as {
+  prisma: PrismaClient | undefined;
+};
+
+function createPrismaClient() {
+  const adapter = new PrismaMariaDb(process.env.DATABASE_URL!);
+  return new PrismaClient({ adapter });
+}
+
+export const prisma = globalForPrisma.prisma ?? createPrismaClient();
+
+if (process.env.NODE_ENV !== "production") {
+  globalForPrisma.prisma = prisma;
+}