Sink seen/read stories, fix F1 matching, drop East Africa pill

- Sink already-seen and read stories to the bottom of the feed (new SeenStory
  model + per-load snapshot so order is stable while scrolling and refreshes
  sink what you've seen) so fresh content surfaces.
- F1 matching: clear F1 headline OR a majority of F1-feed sources, replacing the
  broad keyword list that leaked crypto in (fia -> "deFIAnt"). Dropped unused
  matchSources path.
- Remove the East Africa pill.

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

Jarvis/JarvisApp.swift

@@ -51,6 +51,7 @@ struct JarvisApp: App {
                 await notifications.bootstrap()
             }
         }
-        .modelContainer(for: [CachedStory.self, CachedArticle.self, ReadStory.self, SavedStory.self])
+        .modelContainer(for: [CachedStory.self, CachedArticle.self, ReadStory.self,
+                              SavedStory.self, SeenStory.self])
     }
 }