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/Views/Reader/ArticleReaderView.swift

@@ -175,7 +175,7 @@ struct ArticleReaderView: View {
             HStack(spacing: 10) {
                 Text(article.source)
                     .font(.system(size: 11, weight: .bold))
-                    .foregroundStyle(.white)
+                    .foregroundStyle(Palette.primaryText)
                     .lineLimit(1)
                     .padding(.horizontal, 10).padding(.vertical, 5)
                     .background(Palette.orange)