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/Utilities/Extensions/Date+Extensions.swift

@@ -136,6 +136,18 @@ extension Date {
         return formatter.localizedString(for: self, relativeTo: Date())
     }
 
+    var relativeDayDescription: String {
+        let calendar = Calendar.current
+        let days = calendar.dateComponents([.day], from: calendar.startOfDay(for: self), to: calendar.startOfDay(for: Date())).day ?? 0
+        if days == 0 { return String(localized: "date_today") }
+        if days == 1 { return "1d ago" }
+        if days < 31 { return "\(days)d ago" }
+        let months = calendar.dateComponents([.month], from: self, to: Date()).month ?? 0
+        if months < 12 { return "\(max(1, months))mo ago" }
+        let years = calendar.dateComponents([.year], from: self, to: Date()).year ?? 0
+        return "\(max(1, years))y ago"
+    }
+
     var friendlyDescription: String {
         if isToday {
             return String(localized: "date_today")