Rewrite voice agent testing best practices

[scott-lowe-vapi]

Description

• Replace deprecated Test Suites guidance with a five-page Best practices > Testing section for customer support operators and product managers.
• Explain when to use Simulations for full-conversation outcomes and Evals for decisions at specific conversation points.
• Add guidance for risk-based coverage, repeated runs, regression tests, transcript and recording review, and production monitoring.
• Update navigation, redirects, troubleshooting guidance, examples, and docs-assistant context to remove stale Test Suites references.

Testing Steps

• Run the app locally using fern docs dev or navigate to preview deployment
• Ensure that the changed pages and code snippets work

[github-actions]

🌿 Preview your docs: https://vapi-preview-01a06ee1-3ed4-76ed-a81a-6836c33a6d6f.docs.buildwithfern.com

[lightsage-app]

Lightsage docs evals

Result: passed
Staging docs: https://vapi-preview-01a06ee1-3ed4-76ed-a81a-6836c33a6d6f.docs.buildwithfern.com
Commit: 627f6e4

Average score: 100/100
Passed: 3/3

Eval ID	Status	Score	Model	Tools	Docs 404
08e24c18-82a0-45de-abdc-d237bd12bc0f	Pass	100	codex/gpt-5.4	50	2
08e24c18-82a0-45de-abdc-d237bd12bc0f	Pass	100	claude-code/global.anthropic.claude...	11	0
08e24c18-82a0-45de-abdc-d237bd12bc0f	Pass	100	cursor/auto	16	0