feat: East Africa + Southern Africa pills with regional sub-sections

- East Africa pill: merges Uganda + east-africa tags; Uganda pinned first via sub-sections
- Southern Africa pill: covers SA, Namibia, Botswana, Zimbabwe, Zambia, Mozambique; SA/Namibia/Botswana prioritized
- StoryStore.setPill now resets lastSyncedAt to bypass 30s rate-limit on filter switch
- sectionSupplement background fetch populates sparse regional sections in All digest
- SignalFeedView digestContent: flat hero+scroll path for pills without subSections (was showing max 5)
- Theme: removed standalone Uganda pill, wired new sub-section layouts

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

Jarvis/Models/Models.swift

@@ -178,6 +178,9 @@ final class CachedStory {
     var consensus: String?
     var conflict: String?
     var updatedAt: Date
+    /// Original publish timestamp. Defaults to updatedAt for rows cached before
+    /// this field was added — SwiftData handles the automatic migration.
+    var createdAt: Date = Date()
     var cachedAt: Date
 
     init(from summary: StorySummary) {
@@ -191,6 +194,7 @@ final class CachedStory {
         self.consensus = summary.consensus
         self.conflict = summary.conflict
         self.updatedAt = summary.updatedAt
+        self.createdAt = summary.createdAt
         self.cachedAt = Date()
     }
 }