docs: package Python Exam Practice for discovery

[Xiaotian69]

What changed

• Rewrites the README around the verified 151-question browser practice experience
• Corrects stale paths and local-preview instructions
• Adds four real screenshots, including a successful Pyodide code run
• Adds deterministic Python-blue/yellow hero and 1280×640 Social Preview assets
• Adds an MIT license with a third-party source-content boundary

Why

The prior README referenced directories and scripts that no longer exist and did not show the working product or its browser-based code runner.

Validation

• Verified 151 questions from the committed JSON data
• 5/5 JavaScript syntax checks and 3/3 JSON parses passed
• Local and live pages returned HTTP 200
• Actual Pyodide sample and hidden tests passed in the browser
• Markdown links and image dimensions passed
• Independent specification and quality reviews passed

No application code or question data changed.