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>

parser.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"encoding/json"
 	"encoding/xml"
 	"fmt"
 	"regexp"
@@ -500,3 +501,139 @@ func extractImgTags(html string) []string {
 
 	return urls
 }
+
+// JSON Feed structs (https://jsonfeed.org/version/1.1)
+type JSONFeed struct {
+	Version     string         `json:"version"`
+	Title       string         `json:"title"`
+	HomePageURL string         `json:"home_page_url"`
+	FeedURL     string         `json:"feed_url"`
+	Description string         `json:"description"`
+	Language    string         `json:"language"`
+	Items       []JSONFeedItem `json:"items"`
+}
+
+type JSONFeedItem struct {
+	ID            string           `json:"id"`
+	URL           string           `json:"url"`
+	Title         string           `json:"title"`
+	ContentHTML   string           `json:"content_html"`
+	ContentText   string           `json:"content_text"`
+	Summary       string           `json:"summary"`
+	Image         string           `json:"image"`
+	DatePublished string           `json:"date_published"`
+	DateModified  string           `json:"date_modified"`
+	Authors       []JSONFeedAuthor `json:"authors"`
+	Attachments   []JSONFeedAttachment `json:"attachments"`
+}
+
+type JSONFeedAuthor struct {
+	Name string `json:"name"`
+	URL  string `json:"url"`
+}
+
+type JSONFeedAttachment struct {
+	URL      string `json:"url"`
+	MimeType string `json:"mime_type"`
+	Size     int64  `json:"size_in_bytes"`
+}
+
+func (c *Crawler) parseJSONFeedMetadata(body string, feed *Feed) []*Item {
+	var jf JSONFeed
+	if err := json.Unmarshal([]byte(body), &jf); err != nil {
+		return nil
+	}
+
+	feed.Title = jf.Title
+	feed.Description = jf.Description
+	feed.Language = jf.Language
+	feed.SiteURL = normalizeURL(jf.HomePageURL)
+	feed.ItemCount = len(jf.Items)
+
+	// Parse items
+	now := time.Now()
+	var items []*Item
+	var dates []time.Time
+
+	for _, ji := range jf.Items {
+		item := &Item{
+			FeedURL:      feed.URL,
+			Title:        ji.Title,
+			Link:         ji.URL,
+			DiscoveredAt: now,
+		}
+
+		// Use ID as GUID, fall back to URL
+		if ji.ID != "" {
+			item.GUID = ji.ID
+		} else if ji.URL != "" {
+			item.GUID = ji.URL
+		}
+
+		// Content: prefer HTML, fall back to text
+		if ji.ContentHTML != "" {
+			item.Content = ji.ContentHTML
+		} else if ji.ContentText != "" {
+			item.Content = ji.ContentText
+		}
+		item.Description = ji.Summary
+
+		// Author
+		if len(ji.Authors) > 0 {
+			item.Author = ji.Authors[0].Name
+		}
+
+		// Parse date
+		dateStr := ji.DatePublished
+		if dateStr == "" {
+			dateStr = ji.DateModified
+		}
+		if dateStr != "" {
+			if t, err := time.Parse(time.RFC3339, dateStr); err == nil {
+				item.PubDate = t
+				dates = append(dates, t)
+			}
+		}
+
+		// Images
+		if ji.Image != "" {
+			item.ImageURLs = []string{ji.Image}
+		}
+
+		// Attachments (enclosures)
+		for _, att := range ji.Attachments {
+			if att.URL != "" {
+				item.Enclosure = &Enclosure{
+					URL:    att.URL,
+					Type:   att.MimeType,
+					Length: att.Size,
+				}
+				break // Only use first attachment as enclosure
+			}
+		}
+
+		items = append(items, item)
+	}
+
+	// Calculate date stats
+	if len(dates) > 0 {
+		oldest, newest := dates[0], dates[0]
+		for _, d := range dates {
+			if d.Before(oldest) {
+				oldest = d
+			}
+			if d.After(newest) {
+				newest = d
+			}
+		}
+		feed.OldestItemDate = oldest
+		feed.NewestItemDate = newest
+
+		if len(dates) > 1 {
+			totalHours := newest.Sub(oldest).Hours()
+			feed.AvgPostFreqHrs = totalHours / float64(len(dates)-1)
+		}
+	}
+
+	return items
+}