Add selected GPT-Live guide illustrations

[dev-seth-vapi]

Description

• Add the six approved, code-drawn illustrations to GPT-Live conversation design, tools, migration, and testing guides.
• Keep the drawings free of editorial headings and captions; use short concrete labels and accessible descriptions.
• Supply light/dark and compact layouts that follow the docs theme and phone breakpoint.

Testing Steps

• Validate all 24 SVG variants and image references.
• Review the artwork in light/dark and phone layouts.
• Fern validation: zero errors. Hosted preview checked for page placement, dark-mode switching, and compact layout without horizontal overflow.
• Preview: https://vapi-preview-01a0f535-2a82-71d7-997a-1be5adce6ab1.docs.buildwithfern.com/gpt-live/design
• Verify the production publish and live images after merging.

[lightsage-app]

Lightsage docs evals

Lightsage could not queue docs evals for this PR.

Docs URL: https://vapi-preview-01a0f535-2a82-71d7-997a-1be5adce6ab1.docs.buildwithfern.com/gpt-live/design
Commit: 7c14559
Reason: No custom evals are selected for GitHub PR evals. Open Lightsage > Custom Evals and enable the GitHub checkbox for at least one custom eval.

[github-actions]

🌿 Preview your docs: https://vapi-preview-01a0f536-9cfe-7000-a45c-0d7d1569212e.docs.buildwithfern.com