fix(selectAIProvider): add authorization header for Gemini provider

[krishna2206]

What is this PR about?

When creating a template using AI features and using Gemini, it fails with a 400 error :

Error in suggestVariants: [Error [AI_APICallError]: Bad Request] {
  cause: undefined,
  url: 'https://generativelanguage.googleapis.com/v1beta/chat/completions?key=<GEMINI_API_KEY>',
  requestBodyValues: [Object],
  statusCode: 400,
  responseHeaders: [Object],
  responseBody: '[{\n' +
    '  "error": {\n' +
    '    "code": 400,\n' +
    '    "message": "Missing Authorization header.",\n' +
    '    "status": "INVALID_ARGUMENT"\n' +
    '  }\n' +
    '}\n' +
    ']',
  isRetryable: false,
  data: undefined
}

Checklist

Before submitting this PR, please make sure that:

• You created a dedicated branch based on the canary branch.
• You have read the suggestions in the CONTRIBUTING.md file https://github.com/Dokploy/dokploy/blob/canary/CONTRIBUTING.md#pull-request
• You have tested this PR in your local instance.

[Copilot]

Pull request overview

This PR fixes a 400 "Missing Authorization header" error when using the Gemini AI provider for template creation. The error occurred because Gemini's OpenAI-compatible endpoint requires authentication via an Authorization header with a Bearer token, rather than through query parameters.

• Changed Gemini provider authentication from query parameters to Authorization header with Bearer token format
• Made the configuration consistent with other OpenAI-compatible providers like Perplexity

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