Remove Add Transaction feature and clean all related code

Deleted files:
- AddTransactionView.swift
- TransactionRepository.swift
- Transaction+CoreDataClass.swift

Cleaned files:
- SourceDetailViewModel: removed transactions published property,
  showingAddTransaction flag, transactionRepository dependency,
  addTransaction() and deleteTransaction() methods
- SourceDetailView: removed transactionsSection, TransactionRow struct,
  Add Transaction button from quickActions, sheet presentation
- InvestmentSource+CoreDataClass: removed transactions NSManaged property,
  transactionsArray, totalInvested, totalDividends, totalFees computed
  properties, and all transaction Core Data accessors
- SettingsViewModel: removed "Transaction" from resetAllData entity list
- SampleDataService: removed transactionRepository and sample transaction

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

PortfolioJournal/Views/Dashboard/ShareCards.swift

@@ -7,7 +7,7 @@ struct MonthlyCheckInShareCardView: View {
 
     var body: some View {
         VStack(alignment: .leading, spacing: 14) {
-            Text(summary.periodLabel)
+            Text(summary.formattedMonthYear)
                 .font(.caption.weight(.semibold))
                 .foregroundColor(.white.opacity(0.85))
 
@@ -17,7 +17,9 @@ struct MonthlyCheckInShareCardView: View {
 
             metricRow("Starting", summary.formattedStartingValue)
             metricRow("Ending", summary.formattedEndingValue)
-            metricRow("Contributions", summary.formattedContributions)
+            if summary.contributions != 0 {
+                metricRow("Contributions", summary.formattedContributions)
+            }
             metricRow("Net performance", "\(summary.formattedNetPerformance) (\(summary.formattedNetPerformancePercentage))")
 
             Spacer(minLength: 0)