Allow viewing evolution chart for individual or multiple sources across categories

Adds multi-source selection to the evolution chart source filter.
Users can now tap multiple sources to compare their evolution side by side,
regardless of which category they belong to.

Fixes #24

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

PortfolioJournal/ViewModels/ChartsViewModel.swift

@@ -86,6 +86,7 @@ class ChartsViewModel: ObservableObject {
     @Published var selectedChartType: ChartType = .evolution
     @Published var selectedCategory: Category?
     @Published var selectedSource: InvestmentSource?
+    @Published var selectedSourceIds: Set<UUID> = []
     @Published var selectedTimeRange: TimeRange = .year
     @Published var selectedAccount: Account?
     @Published var showAllAccounts = true
@@ -290,7 +291,12 @@ class ChartsViewModel: ObservableObject {
         }
 
         let sources: [InvestmentSource]
-        if let selectedSource {
+        if !selectedSourceIds.isEmpty {
+            sources = sourceRepository.sources.filter { source in
+                guard let id = source.id else { return false }
+                return selectedSourceIds.contains(id) && shouldIncludeSource(source)
+            }
+        } else if let selectedSource {
             sources = sourceRepository.sources.filter { $0.id == selectedSource.id && shouldIncludeSource($0) }
         } else if let category = category {
             sources = sourceRepository.fetchSources(for: category).filter { shouldIncludeSource($0) }

PortfolioJournal/Views/Charts/ChartsContainerView.swift

@@ -208,18 +208,19 @@ struct ChartsContainerView: View {
                     if availableSources.count > 1 {
                         Button {
                             viewModel.selectedSource = nil
+                            viewModel.selectedSourceIds.removeAll()
                         } label: {
                             Text("All Sources")
                                 .font(.caption.weight(.medium))
                                 .padding(.horizontal, 12)
                                 .padding(.vertical, 6)
                                 .background(
-                                    viewModel.selectedSource == nil
+                                    viewModel.selectedSourceIds.isEmpty && viewModel.selectedSource == nil
                                         ? Color.appPrimary
                                         : Color.gray.opacity(0.1)
                                 )
                                 .foregroundColor(
-                                    viewModel.selectedSource == nil
+                                    viewModel.selectedSourceIds.isEmpty && viewModel.selectedSource == nil
                                         ? .white
                                         : .primary
                                 )
@@ -228,21 +229,28 @@ struct ChartsContainerView: View {
                     }
 
                     ForEach(availableSources, id: \.id) { source in
+                        let sourceId = source.id ?? UUID()
+                        let isSelected = viewModel.selectedSourceIds.contains(sourceId)
                         Button {
-                            viewModel.selectedSource = source
+                            viewModel.selectedSource = nil
                             viewModel.selectedCategory = nil
+                            if isSelected {
+                                viewModel.selectedSourceIds.remove(sourceId)
+                            } else {
+                                viewModel.selectedSourceIds.insert(sourceId)
+                            }
                         } label: {
                             Text(source.name)
                                 .font(.caption.weight(.medium))
                                 .padding(.horizontal, 12)
                                 .padding(.vertical, 6)
                                 .background(
-                                    viewModel.selectedSource?.id == source.id
+                                    isSelected
                                         ? Color.appPrimary
                                         : Color.gray.opacity(0.1)
                                 )
                                 .foregroundColor(
-                                    viewModel.selectedSource?.id == source.id
+                                    isSelected
                                         ? .white
                                         : .primary
                                 )