Add RSS feeds support

[imitation-alpha]

Goal

Add RSS feed support for the static blog so readers can subscribe from standard RSS readers.

Requirements

• Provide RSS 2.0 feeds for:
  • English blog: /blog/feed.xml
  • Traditional Chinese blog: /zh-Hant/blog/feed.xml
  • Site-level default feed: /feed.xml, matching the English blog feed
• Include all current blog posts in reverse chronological order.
• Each feed item should include:
  • post title
  • absolute post URL
  • publication date from article:published_time
  • post description
  • stable guid
  • author name
  • language-appropriate feed metadata
• Add RSS autodiscovery links with rel="alternate" and type="application/rss+xml" to:
  • home page
  • blog index pages
  • individual blog post pages
• Keep the site dependency-free. If automation is needed, use a small script that runs with Python stdlib only.
• Update the README so future blog posts include a step to regenerate or update RSS feeds.

Acceptance Criteria

• /feed.xml, /blog/feed.xml, and /zh-Hant/blog/feed.xml return valid XML when served statically.
• RSS readers can discover the feed from the home page and blog pages.
• Feed item URLs are absolute https://imitation-alpha.github.io/... URLs.
• XML special characters in titles/descriptions are escaped correctly.
• Existing site behavior, theme cookies, blog pages, and relative asset paths are unchanged.