Add provider base URLs for computer use agents

[devin-ai-integration]

Summary

• Adds optional provider-scoped base URL fields for the three computer-use agent API key types: openaiBaseUrl, anthropicBaseUrl, and googleBaseUrl.
• Validates custom API key mode has an apiKeys object and validates supplied base URLs are absolute http/https URLs before sending requests.
• Adds contract tests covering JSON forwarding and local validation for CUA, Claude Computer Use, and Gemini Computer Use.

Review & Testing Checklist for Human

• Confirm the client-side validation behavior is desirable for SDK users, especially requiring apiKeys when useCustomApiKeys is true.
• Verify backend support accepts the new apiKeys.*BaseUrl payload keys for all three endpoints.
• Try one real custom endpoint per provider once backend support is deployed.

Notes

Local checks:

• yarn install
• yarn build
• yarn vitest run tests/sandbox/e2e/computer-use-contract.test.ts
• yarn lint

yarn test was attempted, but the existing full suite requires HYPERBROWSER_API_KEY for sandbox e2e tests and fails before these targeted tests run.

Link to Devin session: https://app.devin.ai/sessions/1ed16d43e37049e8958d37729e8fd6d0
Requested by: @shrisukhani

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[devin-ai-integration]

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.