docs: standardize language, differentiate guides, and add closing notes

[vdusek]

Summary

• Rewrite opening paragraphs for 5 concept pages (proxy management, interacting with other Actors, API access, logging, configuration) to follow a consistent "what it does + why it matters" pattern
• Standardize all 7 guide titles from gerund form ("Using X") to imperative form ("Use X"), including "Running webserver" → "Run a web server"
• Differentiate Playwright and Selenium feature lists — Playwright now highlights auto-waiting, locator API, and network interception; Selenium highlights its broad ecosystem, WebDriver protocol, and flexible selection strategies
• Standardize example intro phrasing to "The following example shows..." across Crawlee, Scrapy, and webserver guides; fix a stray backtick typo in the Crawlee guide
• Remove duplicate opening sentence in the Crawlee guide
• Add closing sentences with API reference/docs links to 5 concept pages that ended abruptly after code blocks

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.64%. Comparing base (b40ad69) to head (c8ddfc9).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #851   +/-   ##
=======================================
  Coverage   86.64%   86.64%           
=======================================
  Files          48       48           
  Lines        2920     2920           
=======================================
  Hits         2530     2530           
  Misses        390      390           

Flag	Coverage Δ
e2e	37.87% <ø> (ø)
integration	59.28% <ø> (ø)
unit	74.69% <ø> (ø)

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