Improve SEO/AEO discovery surface for awesome-python.com (#3103)

* update gitignore

* feat: tighten homepage metadata

* fix: trim generated HTML whitespace

* feat(website): add discovery files and markdown alternate

* feat(website): add sitemap lastmod

* feat(seo): add Content-Signal directive to robots.txt

Signals search, ai-input, and ai-train to crawlers
via the experimental Content-Signal header in robots.txt.

Co-Authored-By: Claude <noreply@anthropic.com>

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Co-authored-by: Claude <noreply@anthropic.com>