Update Python version requirement to match pyproject.toml

The README incorrectly stated Python 3.8+ was sufficient, but
backend/pyproject.toml requires Python >=3.11. This caused
installation errors for users with Python 3.8-3.10.

Fixes #27

Author: nandsha

README.md

@@ -28,7 +28,7 @@ Follow these steps to get the application running locally for development and te
 **1. Prerequisites:**
 
 -   Node.js and npm (or yarn/pnpm)
--   Python 3.8+
+-   Python 3.11+
 -   **`GEMINI_API_KEY`**: The backend agent requires a Google Gemini API key.
     1.  Navigate to the `backend/` directory.
     2.  Create a file named `.env` by copying the `backend/.env.example` file.