Charts: puntos + labels de valor en todas las gráficas de líneas

- Nuevo ChartValueLabels.swift: ChartValueBubble (cápsula) y ChartSelectionCard
  (tarjeta multi-serie), con umbral compartido (<=12 puntos → labels SIEMPRE
  visibles; las gráficas cortas aportan mucho más con los valores a la vista)
- PointMark añadido donde faltaba (Compare, Year vs Year, Drawdown, Volatility);
  agrandado donde ya existía (Evolution, Prediction, Period vs Period, Rolling)
- Selección por tap/arrastre (chartXSelection) en las 8 gráficas: RuleMark + burbuja
  prominente (una serie) o tarjeta con el valor de cada serie (multi-serie)
- Evolution reutiliza su scrubbing existente y ahora muestra burbuja en el punto
- Period vs Period: labels A arriba / B abajo para evitar solapes
- Drawdown/Volatility migrados de Chart(data:) a Chart{ForEach} para poder añadir
  marcas de selección

Verificado en iPad Pro 13" (labels visibles en Evolution y Period vs Period).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015qUZrBusG82T37R7PeokqJ

PortfolioJournal/Views/Charts/PeriodComparisonChartView.swift

@@ -2,6 +2,20 @@ import SwiftUI
 import Charts
 
 struct PeriodComparisonChartView: View {
+    @State private var selectedMonth: Int?
+
+    /// Period charts are short by design (a handful of months) — labels always help.
+    private var showAllLabels: Bool {
+        (viewModel.periodComparisonData.map { $0.points.count }.max() ?? 0) <= ChartLabels.alwaysShowThreshold
+    }
+
+    private func selectionRows(for month: Int) -> [(label: String, value: String, color: Color)] {
+        viewModel.periodComparisonData.compactMap { series in
+            guard let point = series.points.first(where: { $0.monthOffset == month }) else { return nil }
+            return (series.label, ChartLabels.percent(point.returnPct), Color(hex: series.colorHex) ?? .gray)
+        }
+    }
+
     @ObservedObject var viewModel: ChartsViewModel
 
     private let colorA = Color(hex: "#3478F6") ?? .blue
@@ -225,13 +239,35 @@ struct PeriodComparisonChartView: View {
                     y: .value("Return", point.returnPct)
                 )
                 .foregroundStyle(by: .value("Period", point.seriesLabel))
-                .symbolSize(30)
+                .symbolSize(showAllLabels ? 40 : 30)
+                .annotation(position: point.seriesLabel == viewModel.periodComparisonData.first?.label ? .top : .bottom,
+                            spacing: 3) {
+                    if showAllLabels {
+                        ChartValueBubble(
+                            text: ChartLabels.percent(point.returnPct),
+                            color: Color(hex: point.colorHex) ?? .gray
+                        )
+                    }
+                }
             }
 
             RuleMark(y: .value("Zero", 0))
                 .foregroundStyle(Color.secondary.opacity(0.4))
                 .lineStyle(StrokeStyle(lineWidth: 1, dash: [4, 4]))
+
+            if let selectedMonth {
+                RuleMark(x: .value("Selected", selectedMonth))
+                    .foregroundStyle(Color.secondary.opacity(0.35))
+                    .lineStyle(StrokeStyle(lineWidth: 1, dash: [3, 3]))
+                    .annotation(position: .top, spacing: 4) {
+                        ChartSelectionCard(
+                            title: "M\(selectedMonth + 1)",
+                            rows: selectionRows(for: selectedMonth)
+                        )
+                    }
+            }
         }
+        .chartXSelection(value: $selectedMonth)
         .chartForegroundStyleScale(
             domain: viewModel.periodComparisonData.map { $0.label },
             range: seriesColors