Add request body size validation

[meshackyaro]

Description

Large request payloads accepted by SDK but rejected by backend. Should validate size limits client-side.

Component

SDK

Difficulty

🟢 Easy

Tasks

• Add request size validation
• Match backend size limits
• Throw clear error for oversized requests
• Document size limits
• Test with large payloads

Acceptance Criteria

• Oversized requests rejected locally
• Clear error messages
• Limits documented

Estimated Time

1 day