Remove model API key requirement — use only BB API key for session creation

[derekmeegan]

Summary

Removes the Model API Key credential field and all references to modelApiKey / x-model-api-key. The Stagehand API no longer requires a separate model API key — only the Browserbase API key is needed for session creation and agent execution.

Changes

credentials/BrowserbaseApi.credentials.ts

• Removed the modelApiKey credential property (was required, type: password)
• Removed x-model-api-key header from the authenticate config
• Users now only need to provide their BB API Key and Project ID

nodes/Browserbase/Browserbase.node.ts

• Removed x-model-api-key from the request headers object
• Removed apiKey from the /v1/sessions/start request body
• Removed apiKey from the agentConfig.model in the /v1/sessions/{id}/agentExecute request body

package.json

• Version bump: 1.1.3 → 1.2.0

Impact

This is a breaking change for existing users who have the node installed — they will need to re-enter their credentials (since the credential schema changed), but they'll no longer need a model API key at all. Simpler setup overall.