Add RSS feed ingestion

[MakiDevelop]

What needs to be done

Extend ingest.py to accept RSS feed URLs and automatically extract article links from the feed.

Which file(s) to modify

• ingest.py — add RSS parsing logic

Proposed approach

1. Detect if an input URL is an RSS/Atom feed (check Content-Type or try parsing as XML)
2. Parse the feed using xml.etree.ElementTree (stdlib, no new dependencies)
3. Extract <link> elements from each <item> / <entry>
4. Pass extracted URLs through the existing normalize_url() → ingest_urls() flow

Example usage

python3 ingest.py https://simonwillison.net/atom/everything/
python3 ingest.py --rss https://news.ycombinator.com/rss

Acceptance criteria

• RSS and Atom feeds are both supported
• Uses only stdlib (xml.etree.ElementTree)
• Falls back gracefully if URL is not a valid feed
• Adds tests in tests/test_ingest.py