docs: add Crawl4AI guide

[vdusek]

Adds a guide for using the Crawl4AI LLM-friendly web crawler in Apify Actors, following the structure of the existing scraping-library guides (BeautifulSoup, Playwright, Scrapy).

What's included

• docs/03_guides/10_crawl4ai.mdx — the guide: introduction & features, a runnable example Actor that crawls pages into LLM-ready markdown, Apify Proxy integration, and the Dockerfile / base-image setup for running the browser on the platform.
• docs/03_guides/code/crawl4ai_project/ — the example Actor: a recursive markdown scraper using Crawl4AI's AsyncWebCrawler through Apify Proxy, plus its Dockerfile.
• Link to the new guide added to the quick-start "Guides" list.
• pyproject.toml — a ruff I001 per-file-ignore for the new code project (matches the existing Scrapy ignore).

Notes

• Built on the Python 3.13 Playwright base image: Crawl4AI pins lxml < 6, which has no cp314 wheels yet, so the 3.14 image would force a slow source build. Crawl4AI reuses the base image's pre-installed browser, so no extra browser-install step is needed in the Dockerfile.

Verification

• The example Actor was run locally (apify run) and on the Apify platform (build + run SUCCEEDED), producing dataset items with url / title / markdown.
• Apify Proxy confirmed: requests egress through an Apify Proxy IP, distinct from the direct IP.
• ruff format --check, ruff check, and ty check pass.

Numbered 10 to sit after the in-progress uv (#932 → 08) and Scrapling (#938 → 09) guides.

Part of #836.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.98%. Comparing base (3f25d4a) to head (a62a06b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #942      +/-   ##
==========================================
+ Coverage   86.87%   86.98%   +0.10%     
==========================================
  Files          48       48              
  Lines        2942     2942              
==========================================
+ Hits         2556     2559       +3     
+ Misses        386      383       -3     

Flag	Coverage Δ
e2e	37.76% <ø> (ø)
integration	59.14% <ø> (+0.03%)	⬆️
unit	75.69% <ø> (+0.06%)	⬆️

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