fix: improve API validation error messages with request context

[CaralHsi]

Summary

• Enhanced validation_error_handler in exceptions.py to include request method, path, and human-readable error descriptions in both the response message and server logs
• Callers can now immediately identify which endpoint failed and what fields are missing, without needing to check server logs

Closes #1349

Test Plan

• Send POST /product/get_memory with empty body → response message includes POST /product/get_memory: [body] Field required (type: missing)
• Send POST /product/get_memory with body missing mem_cube_id → response message includes [body -> mem_cube_id] Field required (type: missing)
• Normal valid requests are not affected