fix: display story age from firstSeenAt, not updatedAt

Old stories were reading "1 hr ago" because updatedAt bumps every time
the backend attaches another article to a cluster, however loosely
related. firstSeenAt is when the cluster actually first appeared and
is already in the API response — just wasn't decoded.

Verified live: story_1a37c858235b (F1 Austria GP recap) has
firstSeenAt 2026-06-16 but updatedAt 2026-07-11, freshnessScore 0.96 —
looked brand new despite being 25 days old. Also confirmed the API's
isStale field is unusable as a stopgap (always false regardless of age).

Ranking still surfaces old stories at the top — that's server-side
(signalScore/freshnessScore) and out of scope for the client per the
architecture rule against re-ranking. Logged in BACKLOG #15.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Jarvis/Views/Home/StoryRowView.swift

@@ -99,7 +99,11 @@ struct StoryRowView: View {
 
     private var metaLine: String {
         let sources = "\(story.sourceCount) source\(story.sourceCount == 1 ? "" : "s")"
-        return "\(sources) · \(Topic.label(story.topic)) · \(story.updatedAt.timeAgoShort()) ago"
+        // firstSeenAt is when the cluster appeared — updatedAt bumps on every
+        // article the backend attaches, so it can read "just now" on stories
+        // that are actually weeks old.
+        let age = (story.firstSeenAt ?? story.updatedAt).timeAgoShort()
+        return "\(sources) · \(Topic.label(story.topic)) · \(age) ago"
     }
 }
 
@@ -117,7 +121,8 @@ struct StoryRowView: View {
                     id: "\(score)", headline: "Bank of Uganda cuts interest rates by 50 basis points",
                     summary: "", topic: "finance", tags: ["finance"], signalScore: score, scoreBreakdown: breakdown,
                     sourceCount: 7, sources: sources, consensus: nil, conflict: nil,
-                    updatedAt: Date().addingTimeInterval(-3600), createdAt: Date()),
+                    updatedAt: Date().addingTimeInterval(-3600), createdAt: Date(),
+                    firstSeenAt: Date().addingTimeInterval(-3600)),
                 isCached: score == 64
             )
         }