fix: migrate to Prisma 7 driver adapter (libsql) for SQLite

Prisma 7 removed support for `url` in schema.prisma datasources and the
`engineType = "library"` native binary engine. All connections now go
through a driver adapter.

- Remove engineType and url from schema.prisma (no longer supported)
- Configure prisma.config.ts with migrate.adapter using @libsql/client
- Instantiate PrismaClient with PrismaLibSQL adapter in src/lib/prisma.ts
- Add @libsql/client and @prisma/adapter-libsql dependencies
- Remove PRISMA_CLIENT_ENGINE_TYPE from Dockerfile (obsolete)

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

prisma.config.ts

@@ -1,9 +1,16 @@
 import "dotenv/config";
-import { defineConfig, env } from "prisma/config";
+import { defineConfig } from "prisma/config";
+import { createClient } from "@libsql/client";
+import { PrismaLibSQL } from "@prisma/adapter-libsql";
 
 export default defineConfig({
   schema: "prisma/schema.prisma",
-  datasource: {
-    url: env("DATABASE_URL") || "file:./dev.db",
+  migrate: {
+    adapter: async () => {
+      const libsql = createClient({
+        url: process.env.DATABASE_URL ?? "file:./dev.db",
+      });
+      return new PrismaLibSQL(libsql);
+    },
   },
 });