Fix build errors for Next.js 16 + Prisma 7

- Fix Prisma import: use @/generated/prisma alias (resolves Turbopack issue)
- Replace middleware.ts with proxy.ts (Next.js 16 convention)
- middleware function renamed to proxy

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/prisma.ts

@@ -1,4 +1,4 @@
-import { PrismaClient } from "../generated/prisma";
+import { PrismaClient } from "@/generated/prisma";
 
 const globalForPrisma = globalThis as unknown as {
   prisma: PrismaClient | undefined;