feat: add AI Gateway support to @netlify/dev for Vite plugin

[kathmbeck]

Added AI Gateway bootstrap support to @netlify/dev package:

• Adds @netlify/ai as dep
• Fetches AI gateway token
• Parses the AI gateway context and injects the provider environment variables via runtime.env.set()

Tested with dogs-explorer template referenced on ticket with debug logs and by manually patching node modules to include the AI Gateway bootstrap logic:
https://github.com/netlify-templates/dogs-explorer
https://linear.app/netlify/issue/RUN-2155/support-ai-gateway-bootstrap-in-our-vite-plugin

Running npm run dev

11:48:35 PM [vite] ⬥ Netlify [AI Gateway] Fetching token...
11:48:35 PM [vite] ⬥ Netlify [AI Gateway] Environment variables set
11:48:35 PM [vite] ⬥ Netlify Environment loaded

Verified env vars present in function with curl to test function

{
  "OPENAI_API_KEY": "SET",
  "AI_GATEWAY": "SET"
}

[rybit]

did we change this to NETLIFY_AI_GATEWAY https://docs.netlify.com/build/ai-gateway/overview/

NETLIFY_AI_GATEWAY_KEY and NETLIFY_AI_GATEWAY_BASE_URL environment variables are always injected into the AI Gateway-supported runtimes. If you want to mix different setups with your own keys and Netlify’s or you want to be explicit about using AI Gateway keys in your calls, use these env variables as they will never collide with other environment variables values.

[kathmbeck]

Ah good catch that we need to set it, but it would be where we decode the context stored in AI_GATEWAY and set all the env vars. Added it to main.ts.