Create Driver model in Prisma

**Title:** Create Driver model in Prisma

**Description:**
• Add a new model called Driver in apps/backend/prisma/schema.prisma.
• Fields:
• id: Integer, primary key, autoincremented
• name: String, required
• point: Integer, required
• seriesId: Integer, required (relation to Series)
• team: String, required
• nationality: String, required

**Relations:**
• series: Connect Driver to a Series (many drivers belong to one series).
• Also prepare for future relation with Session (a driver can participate in multiple sessions).

**Acceptance Criteria:**
• Prisma schema compiles without errors.
• prisma generate works after editing.