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/Views/Shared/Theme.swift

@@ -188,25 +188,35 @@ struct Interest: Identifiable, Hashable {
     /// When set, matches the backend topic classification instead of keywords
     /// (e.g. finance, tech).
     var topicSlug: String? = nil
-    /// Whether to consider source/outlet names when matching. True only for F1
-    /// (its sources are the signal). Regions must NOT — an outlet's location is
-    /// not the story's location (e.g. a Congo story carried by an SA outlet).
-    var matchSources: Bool = false
-
     func matches(_ s: StorySummary) -> Bool {
+        if id == "f1" { return Interest.isFormula1(s) }
         if let topicSlug {
             return s.topic.caseInsensitiveCompare(topicSlug) == .orderedSame
         }
-        // Headline only — the backend's summaries are polluted by over-clustering
-        // (a Congo headline can carry a South-Africa summary), so they're unsafe
-        // to match on. F1 additionally trusts its (clean) source names.
-        var hay = s.headline
-        if matchSources { hay += " " + s.sources.map(\.name).joined(separator: " ") }
-        hay = hay.lowercased()
+        // Headline only — the backend's summaries/outlet names are polluted by
+        // over-clustering (a Congo headline can carry a South-Africa summary or an
+        // SA outlet), so they're unsafe to match on.
+        let hay = s.headline.lowercased()
         if excludeKeywords.contains(where: { hay.contains($0) }) { return false }
         return keywords.contains { hay.contains($0) }
     }
 
+    /// F1 = a clear F1 headline, or a majority of F1-feed sources. A single F1
+    /// source isn't enough — the over-clustered backend sometimes attaches one to
+    /// an unrelated story. Avoids substring traps like "fia" matching "deFIAnt".
+    static func isFormula1(_ s: StorySummary) -> Bool {
+        let h = s.headline.lowercased()
+        if h.contains("formula 1") || h.contains("formula one") || h.contains("grand prix")
+            || h.hasPrefix("f1 ") || h.hasSuffix(" f1") || h.contains(" f1 ") || h.contains("f1:") {
+            return true
+        }
+        let feeds = ["f1", "racefans", "motorsport", "autosport", "planetf1", "the race", "formula 1"]
+        let srcs = s.sources
+        guard !srcs.isEmpty else { return false }
+        let n = srcs.filter { src in feeds.contains { src.name.lowercased().contains($0) } }.count
+        return Double(n) / Double(srcs.count) >= 0.5
+    }
+
     // Region keywords are place/person names found in the story text — never
     // outlet names (which are unreliable due to backend over-clustering).
     private static let ugandaKeywords = ["uganda", "ugandan", "kampala", "museveni",
@@ -216,22 +226,12 @@ struct Interest: Identifiable, Hashable {
                                               "eskom", "gauteng", "western cape", "soweto",
                                               "drakensberg", "mbalula", "zuma"]
 
-    static let f1 = Interest(id: "f1", label: "F1",
-        keywords: ["formula 1", "formula one", "grand prix", "f1", "verstappen", "hamilton",
-                   "mclaren", "ferrari", "red bull", "racefans", "motorsport", "autosport",
-                   "pole position", "pirelli", "qualifying", "fia", "planetf1"],
-        matchSources: true)
+    static let f1 = Interest(id: "f1", label: "F1")   // matching handled by isFormula1
 
-    /// Pinned filter pills, in order. Regions are mutually exclusive.
+    /// Pinned filter pills, in order.
     static let pinned: [Interest] = [
         f1,
         Interest(id: "uganda", label: "Uganda", keywords: ugandaKeywords),
-        Interest(id: "east-africa", label: "East Africa",
-                 keywords: ["east africa", "eastafrican", "kenya", "kenyan", "nairobi",
-                            "tanzania", "tanzanian", "dar es salaam", "rwanda", "rwandan",
-                            "kigali", "ethiopia", "ethiopian", "addis ababa", "burundi",
-                            "south sudan", "juba"],
-                 excludeKeywords: ugandaKeywords + southAfricaKeywords),
         Interest(id: "south-africa", label: "South Africa", keywords: southAfricaKeywords),
         Interest(id: "finance", label: "Finance", topicSlug: "finance"),
         Interest(id: "tech", label: "Tech", topicSlug: "tech"),