Incorrect documentation paths referenced in llms.txt

[GBLightning]

Description
Several documentation links in llms.txt point to non-existing or outdated paths.

To Reproduce
Open llms.txt, scroll to the Documentation section at the end of the file, and try opening the listed links.

Expected behavior
All links should lead to existing documentation files.

Additional context

1. https://github.com/google/adk-docs/blob/main/docs/agents/models.md - was removed because it was only a template.
2. https://github.com/google/adk-docs/blob/main/docs/deploy/agent-engine.md - was separated into several .md files - docs/deploy/agent-engine/asp.md, docs/deploy/agent-engine/deploy.md, docs/deploy/agent-engine/index.md, docs/deploy/agent-engine/test.md.
3. https://github.com/google/adk-docs/blob/main/docs/get-started/testing.md - was renamed (C099) to docs/runtime/api-server.md
4. https://github.com/google/adk-docs/blob/main/docs/streaming/custom-streaming-ws.md - was removed.
5. https://github.com/google/adk-docs/blob/main/docs/streaming/custom-streaming.md - was removed.
6. https://github.com/google/adk-docs/blob/main/docs/tools/authentication.md - was moved (R100) to docs/tools-custom/authentication.md
7. https://github.com/google/adk-docs/blob/main/docs/tools/built-in-tools.md - was reorganized and separated into several files.
8. https://github.com/google/adk-docs/blob/main/docs/tools/function-tools.md - was moved (R099) to docs/tools-custom/function-tools.md
9. https://github.com/google/adk-docs/blob/main/docs/tools/google-cloud-tools.md - was moved (R074) to docs/tools/google-cloud/application-integration.md
10. https://github.com/google/adk-docs/blob/main/docs/tools/mcp-tools.md - was moved (R100) to docs/tools-custom/mcp-tools.md
11. https://github.com/google/adk-docs/blob/main/docs/tools/openapi-tools.md - was moved (R100) to docs/tools/third-party/openapi-tools.md
12. https://github.com/google/adk-docs/blob/main/docs/tools/third-party-tools.md - was moved (R100) to docs/tools/third-party/index.md

[llalitkumarrr]

Hello @GBLightning ,

This issue should be fixed with PR #4163, please feel free to reach out if you still have any questions.

[adk-bot]

This issue has been automatically marked as stale because it has not had recent activity for 7 days after a maintainer requested clarification. It will be closed if no further activity occurs within 7 days.