feat: implement role-based authentication with Passport JWT

[Spycall]

• Add UserRole enum (INVESTOR, CREATOR, ADMIN) to Prisma schema
• Add role field to User model with default INVESTOR role
• Install @nestjs/passport, passport, passport-jwt dependencies
• Create JWT strategy for token validation
• Create Roles decorator and RolesGuard for role-based access control
• Create AuthModule with JWT configuration
• Update admin routes (/admin/*) to require JWT auth + ADMIN role
• Update institutional routes (/institutional) to require JWT auth + ADMIN role
• Update user freeze request review endpoint to require JWT auth + ADMIN role
• Integrate AuthModule into main AppModule

This implements secure, token-based session management that distinguishes between Investor, Creator, and Admin roles, protecting sensitive admin and internal routes.

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Issue	Title
#357	Implement JWT-based Role Access Control (RBAC)	Link to this issue
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[Spycall]

Closes #503