Remove Web Search Tool from Prompt Agent

[nitya]

The web search tool conflicts with the grounded data.
https://github.com/nitya/agent-optimization-workshop/blob/main/labs/fundamentals/04-create-prompt-agent.md

We should do the following

1. Initially search with default = shows web searches (not grounded)
2. Add data files now to ground it = shows mixture of web and data
3. OPTIMIZE = either remove web search or optimize instructions to describe when to use what

[nitya]

Tracked in the Code Club walkthrough: #4 — verified at checklist items A4 (portal prompt agent, incl. the default → grounded → optimize progression as A4a/A4b/A4c), B5 (CLI/agent.yaml tool config parity), and A10 / B10 (the optimize lab where web search is removed or scoped by instruction).

[nitya]

Fix made in working branch. PR pending