Add AI-Generated Eco News Feature to Manage Eco News Page

[Maryna-511750]

As a GreenCity admin I want to add an AI-generated Eco News feature to the "Manage Eco News" page so that I can easily create new Eco News articles using artificial intelligence.

Assumptions & Constraints

1. Assumption: The AI endpoint /ai/generate/eco-news is already implemented and functional.
2. Assumption: The endpoint supports requests both with and without a topic parameter.
3. Dependency: The AI service must be accessible and return responses in a reasonable time.

Business rules

1. If the AI endpoint returns an error, a user-friendly error message must be displayed.
2. Users must have the option to edit the AI-generated text before submission.

Acceptance Criteria

• A new button labeled "Generate AI Eco News" is added to the "Add Eco News" form.
• Clicking the button opens a modal or input field where the user can optionally provide a topic for the Eco News.
• If a topic is provided, a request is sent to /ai/generate/eco-news with the topic as a parameter.
• If no topic is provided, a request is sent to /ai/generate/eco-news without a topic.
• The AI-generated text is displayed in the Eco News form for review and editing.
• Errors during the AI generation process are handled gracefully, with clear feedback to the user.

Epic link
Epic #910 [Epic] (#910)