rss generator that creates rss feeds for non-rss blogs

1. Add a new entry to /blogs.json with CSS selectors
2. The cron job will automatically pick it up on the next run or run it manually in generateFeed.cron.ts
3. Feed will be available at /rss/<your-slug>.xml

• Uses Val Town Blob Storage with single key per feed: rss_{slug}.xml
• Metadata stored as meta_{slug} with generation timestamps and post counts
• Feeds are updated only on successful scrapes
• Stale feeds are served indefinitely until next successful update