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/Store/CacheMaintenance.swift

@@ -10,11 +10,8 @@ enum CacheMaintenance {
     private static let hour: TimeInterval = 3_600
     private static let day: TimeInterval = 86_400
 
-    // Aligned to the backend's aging model:
-    //   RECENT_HOURS = 72  → active feed window; drop cached stories past it
-    //   raw-article retention ~14 days → match for cached article bodies
-    private static let recentHours = 72.0    // backend active window (story list)
-    private static let markerHours = 96.0    // seen/read markers: active window + buffer
+    private static let recentHours = 84.0    // 3.5 days: survives weekends
+    private static let markerHours = 96.0   // 4 days: active window + buffer
     private static let articleDays = 14.0    // cached article bodies (backend article retention)
 
     /// Age-based eviction. Run on launch. Cheap; protects saved stories.