Add Organization Bank Account CRUD Endpoints

[grantfox-oss]

Description:
BankAccount exists in Prisma, but there are no API routes to manage it. Implement bank account CRUD routes and service methods for organizations to manage payment destinations securely.

[GBOYEE]

Hi! I'd like to work on this issue.

I have experience with this stack and can deliver a clean, tested solution. Please assign this to me and I'll submit a PR shortly.

My approach:

• Analyze the root cause
• Implement a fix following existing code patterns
• Add tests and documentation

Thanks!