feat: add OpenAI and Anthropic provider metadata

[ishwarthecodddr]

Summary

fixes:#1299

Adds comprehensive provider metadata for OpenAI and Anthropic LLM providers to enable proper integration, error messaging, and user guidance.

Changes

• ✅ Added OpenAI provider details in provider-details.ts:

  • API key environment variable: OPENAI_API_KEY
  • Config key: llm.openaiApiKey
  • Signup link: https://platform.openai.com/api-keys
  • Documentation: https://platform.openai.com/docs/guides/error-codes

• ✅ Added Anthropic provider details in provider-details.ts:

  • API key environment variable: ANTHROPIC_API_KEY
  • Config key: llm.anthropicApiKey
  • Signup link: https://console.anthropic.com/settings/keys
  • Documentation: https://docs.anthropic.com/en/api/errors

• ✅ Updated provider-details.spec.ts to include both new providers in the test expectations

Testing

• ✅ All 226 tests pass
• ✅ TypeScript compilation successful
• ✅ Build completes without errors
• ✅ Changeset created

This enables:

• Proper error messages showing correct environment variable names
• User guidance with links to get API keys
• Consistent troubleshooting documentation
• Complete provider discovery and validation