feat: Add high-fidelity "Save as PDF" using Playwright

[kalmastenitin]

This PR implements a robust "Save as PDF" feature that allows users to download Medium articles as high-quality PDF documents.

Unlike standard HTML-to-PDF converters, this implementation uses Playwright (Headless Chromium) to render the page. This ensures that the PDF looks exactly like the browser's "Print" view ("Ctrl+P"), preserving:

✅ Syntax Highlighting (Code blocks retain colors/formatting).
✅ Complex Layouts (Images, blockquotes, and headers render correctly).
✅ Fonts & Typography (Matches the web reading experience).

Technical Changes
Backend (server/handlers/main.py):

• Added a new endpoint: GET /render_pdf/{path}.
• Implemented render_pdf using async_playwright.
• Injecting custom print CSS to hide navbars, buttons, and footers before rendering.

Docker (Dockerfile):

• Replaced weasyprint dependencies with playwright.
• Added installation of Chromium browser and system dependencies.
• Configured a shared PLAYWRIGHT_BROWSERS_PATH for the freedium user.

Dependencies:
Added: playwright.

How to Test

Rebuild the container to install browsers:
docker compose up --build --no-cache
Navigate to any article.
Use the button : Near Free No. section: PDF