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/schema.prisma

@@ -2,13 +2,11 @@
 // learn more about it in the docs: https://pris.ly/d/prisma-schema
 
 generator client {
-  provider   = "prisma-client-js"
-  engineType = "library"
+  provider = "prisma-client-js"
 }
 
 datasource db {
   provider = "sqlite"
-  url      = env("DATABASE_URL")
 }
 
 model Account {