[Agent Builder] Document human-in-the-loop confirmation for custom tools

[charlotte-hoblik]

Documents the Require user confirmation policy for custom tools, added in elastic/kibana#281896 (9.6).

Changes

• custom-tools.md — replaces the "not available" note; explains that the policy is configurable in the UI for workflow and MCP tools, and via the Tools API for any custom tool type
• workflow-tools.md, mcp-tools.md — new Require user confirmation configuration entry; both screenshots recaptured to show the control
• chat.md — generalizes tool confirmation beyond Elastic-built tools, adds an example of the generic prompt, adds the missing serverless: ga badge
• limitations-known-issues.md — clarifies that a declined tool call does not fail the sub-agent run
• agent-builder-api-tutorial.md — drops the now-inaccurate "Elastic-built" qualifier

Scoped stack: ga 9.6+ / serverless: ga.

Closes elastic/docs-content-internal#1610

[github-actions]

Elastic Docs AI PR menu

Check the box to run an AI review for this pull request.

• Review docs changes (docs-review). Status: not started.

Powered by GitHub Agentic Workflows and docs-actions. For more information, reach out to the docs team.

[github-actions]

🔍 Preview links for changed docs

• explore-analyze/ai-features/agent-builder/agent-builder-api-tutorial.md
• explore-analyze/ai-features/agent-builder/chat.md
• explore-analyze/ai-features/agent-builder/limitations-known-issues.md
• explore-analyze/ai-features/agent-builder/tools/custom-tools.md
• explore-analyze/ai-features/agent-builder/tools/mcp-tools.md
• explore-analyze/ai-features/agent-builder/tools/workflow-tools.md

[github-actions]

✅ Elastic Docs Style Checker (Vale)

No issues found on modified lines!

---

The Vale linter checks documentation changes against the Elastic Docs style guide. To use Vale locally or report issues, refer to Elastic style guide for Vale.

[leemthompo]

Nice! LGTM