[CHORE]: Part 2: Replace Raw Errors with Friendly Messages in main.py

[rakdutta]

The original issue #363 has been closed after covering several routers. However, a few endpoints in main.py still return raw technical errors. This issue aims to address those remaining routers by improving their error handling and ensuring they return user-friendly messages

Update the following router functions in main.py:

update_gateway

update_prompt

update_tool

create_prompt

create_tool

📌 Expected Improvements:
Catch common exceptions (e.g., ValidationError, IntegrityError, Exception)

Return structured responses with clear error messages

Avoid exposing raw traceback or technical details to the user