Add JSON Feed support

- Detect JSON Feed format (jsonfeed.org) via version field
- Parse JSON Feed metadata and items
- Support application/feed+json MIME type for feed discovery
- Include "json" as valid feed type (not auto-denied)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

feed.go

@@ -178,12 +178,12 @@ type Feed struct {
 // saveFeed stores a feed in PostgreSQL
 func (c *Crawler) saveFeed(feed *Feed) error {
 	// Default publishStatus to "held" if not set
-	// Auto-deny feeds with no language or non-RSS/Atom type
+	// Auto-deny feeds with no language or unsupported type
 	publishStatus := feed.PublishStatus
 	if publishStatus == "" {
 		if feed.Language == "" {
 			publishStatus = "deny"
-		} else if feed.Type != "rss" && feed.Type != "atom" {
+		} else if feed.Type != "rss" && feed.Type != "atom" && feed.Type != "json" {
 			publishStatus = "deny"
 		} else {
 			publishStatus = "held"
@@ -779,6 +779,8 @@ func (c *Crawler) processFeed(feedURL, sourceHost, body string, headers http.Hea
 		items = c.parseRSSMetadata(body, feed)
 	case "atom":
 		items = c.parseAtomMetadata(body, feed)
+	case "json":
+		items = c.parseJSONFeedMetadata(body, feed)
 	}
 
 	// Refine category based on parsed title (e.g., "Comments on:")
@@ -951,6 +953,8 @@ func (c *Crawler) CheckFeed(feed *Feed) (bool, error) {
 		items = c.parseRSSMetadata(body, feed)
 	case "atom":
 		items = c.parseAtomMetadata(body, feed)
+	case "json":
+		items = c.parseJSONFeedMetadata(body, feed)
 	}
 
 	// Content changed - reset backoff