fix: RSS feed now shows newest posts first

Fixed bug where feedgen library was reversing the order of feed items.
Database returns notes in DESC order (newest first), but feedgen was
displaying them oldest-first in the RSS XML. Added reversed() wrapper
to maintain correct chronological order in the feed.

Added regression test to verify feed order matches database order.

Bug confirmed by testing:
- Database: [Note 2, Note 1, Note 0] (newest first)
- Old feed: [Note 0, Note 1, Note 2] (oldest first) ❌
- New feed: [Note 2, Note 1, Note 0] (newest first) ✅

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

starpunk/feed.py

@@ -92,8 +92,9 @@ def generate_feed(
     # Set last build date to now
     fg.lastBuildDate(datetime.now(timezone.utc))
 
-    # Add items (limit to configured maximum)
-    for note in notes[:limit]:
+    # Add items (limit to configured maximum, newest first)
+    # Notes from database are DESC but feedgen reverses them, so we reverse back
+    for note in reversed(notes[:limit]):
         # Create feed entry
         fe = fg.add_entry()