Cache backend tags so offline pill filtering stays accurate

Add tags[] to CachedStory (defaulted for lightweight migration) and persist
them on upsert; offline StorySummary now carries the cached tags instead of
falling back to topic. Backend stays the source of truth.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Jarvis/Models/Models.swift

@@ -170,6 +170,9 @@ final class CachedStory {
     var headline: String
     var summary: String
     var topic: String
+    /// Canonical backend tags, so offline pill filtering stays accurate.
+    /// Defaulted for lightweight migration of existing cached rows.
+    var tags: [String] = []
     var signalScore: Int
     var sourceCount: Int
     var consensus: String?
@@ -182,6 +185,7 @@ final class CachedStory {
         self.headline = summary.headline
         self.summary = summary.summary
         self.topic = summary.topic
+        self.tags = summary.tags ?? []
         self.signalScore = summary.signalScore
         self.sourceCount = summary.sourceCount
         self.consensus = summary.consensus