Create a single-page Single Page Application (SPA) using HTML, CSS, and JavaScript. The SPA should function as an AI-generated text detector for legal documents. It needs to:
1. **User Interface:**
* A prominent title: 'AI Legal Document Authenticator'.
* A large, multi-line text area where users can paste or type text from a legal document.
* A button labeled 'Analyze Document'.
* A clear, designated area below the button to display the analysis results (e.g., 'Confidence Score: XX%', 'Potential AI Generation Indicators: [List]', 'Authenticity Status: Verified/Unverified/Inconclusive').
* A placeholder for uploading a document file (though for MVP, direct text input is sufficient, but UI should accommodate this for future).
* A simple, professional, and clean design. Use a neutral color palette (e.g., blues, grays, whites).
2. **Functionality (Client-side simulation for MVP):**
* When the 'Analyze Document' button is clicked, simulate an analysis process.
* For this MVP, instead of complex AI models, implement a *simulated* detection logic. This logic should randomly generate a 'Confidence Score' between 10% and 95% (e.g., 45.7%, 88.2%, 23.9%).
* Based on the generated score, provide a 'Potential AI Generation Indicators' list. These indicators should be pre-defined and appear more frequently for lower confidence scores. Examples: 'Unusual phrasing complexity', 'Lack of specific legal jargon context', 'Repetitive sentence structures', 'Overly formal or generic tone'.
* Determine 'Authenticity Status':
* If score > 75%, 'Verified'.
* If score < 40%, 'Unverified'.
* Otherwise, 'Inconclusive'.
* The results should be displayed dynamically in the designated area.
3. **Technical Requirements:**
* Use standard HTML5 for structure.
* Use CSS for styling. No external CSS frameworks like Bootstrap or Tailwind are allowed for this specific task. Write custom CSS.
* Use vanilla JavaScript for all interactivity and simulated logic. No external JavaScript libraries (like jQuery) are allowed.
* The entire application must be self-contained within a single HTML file.
4. **Focus:** The primary goal is to demonstrate the *concept* of such a tool through a functional front-end prototype. The 'AI detection' part is simulated for this MVP.