Refactor error handling to use Result type pattern instead of exceptions

[Smartdevs17]

Description

Services throw exceptions for expected error cases, making error handling unpredictable. Refactor to use Result/Option types for explicit error handling.

Acceptance Criteria

• Result<T, E> type defined with proper TypeScript typing
• All service methods return Result types
• Controllers map Result to HTTP responses
• Exception handling only for unexpected errors
• Migration guide for existing code

Technical Scope

• packages/types/src/exports.ts
• backend/src/services/
• Edge: async Result handling, error type hierarchy, interop with third-party libraries