docs: add #1792 tool guardrails to the guardrails document page

[AbdulSamad94]

Please read this first

• Have you read the docs?Agents SDK docs yes
• Have you searched for related issues? yes

Question

Tool input/output guardrails (PR #1792) are implemented but not documented in the main guides.

Gaps

• No mention in docs/guardrails.md
• No user guide for implementing input/output guardrails
• Only a minimal API ref at docs/ref/tool_guardrails.md

Current

• Code: src/agents/tool_guardrails.py
• Example: examples/basic/tool_guardrails.py
• API ref: docs/ref/tool_guardrails.md

Expected

Main docs should explain:

• What tool guardrails are vs. agent-level guardrails
• How to add input & output guardrails
• When/why to use them
• Complete examples & use cases

[seratch]

Thanks for pointing this out. The tool guardrail feature is not yet released, so we can prepare the document updates and merge the changes once it's released.