feat(openrouter): send HTTP-Referer and X-Title headers to identify app

[RomneyDa]

Summary

• Adds HTTP-Referer: https://www.continue.dev/ and X-Title: Continue headers to all OpenRouter API requests, per the OpenRouter docs
• This identifies Continue in OpenRouter's activity dashboard and App Showcase
• User-configured headers in requestOptions.headers take precedence over the defaults

Closes #4049

Test plan

• Verify OpenRouter requests include HTTP-Referer and X-Title headers
• Verify user-configured requestOptions.headers can still override these defaults
• Confirm the OpenRouter activity dashboard shows "Continue" in the App column

---

Summary by cubic

Send HTTP-Referer: https://www.continue.dev/ and X-Title: Continue with all OpenRouter API requests to identify the app in OpenRouter’s dashboard and App Showcase. Headers are injected via requestOptions.headers so they apply to all requests; user-provided headers still override, and the redundant getHeaders() override was removed.

^{Written for commit 2945159. Summary will update on new commits.}

[continue]

Docs Review: No documentation updates needed for this PR.

This change automatically sends HTTP-Referer and X-Title headers to OpenRouter—an internal implementation detail that happens transparently without user configuration. Since users don't need to configure or be aware of these headers (and can still override them via requestOptions.headers as already documented), no docs changes are required.

[continue]

Test Coverage Review

This PR adds new functionality for sending HTTP-Referer and X-Title headers to OpenRouter, but no tests are included for this behavior.

Missing Test Coverage

The following new functionality should have tests:

1. getHeaders() override method - Should verify that:

   • The returned headers include HTTP-Referer: https://www.continue.dev/
   • The returned headers include X-Title: Continue
   • Headers from the parent class (super.getHeaders()) are preserved

2. Constructor header injection - Should verify that:

   • Default OpenRouter headers are added to requestOptions.headers
   • User-provided requestOptions.headers are not overwritten by defaults (user headers take precedence due to spread order)

Suggested Test Cases

describe('OpenRouterApi headers', () => {
  it('includes HTTP-Referer and X-Title in getHeaders', () => {
    const api = new OpenRouterApi({ provider: 'openrouter', apiKey: 'test' });
    const headers = api['getHeaders']();
    expect(headers['HTTP-Referer']).toBe('https://www.continue.dev/');
    expect(headers['X-Title']).toBe('Continue');
  });

  it('allows user headers to override defaults', () => {
    const api = new OpenRouterApi({
      provider: 'openrouter',
      apiKey: 'test',
      requestOptions: {
        headers: { 'X-Title': 'Custom App' }
      }
    });
    // Verify custom header takes precedence
  });
});

Please add tests for the header functionality to packages/openai-adapters/src/apis/OpenRouter.test.ts.

[cubic-dev-ai]

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