1.5.0: aviso de huecos + resumen mensual compartible + import con vista previa

Feature 1 — Aviso de huecos: SnapshotGapDetector detecta huecos internos por
source (meses sin datos entre dos snapshots). Banner desechable en Dashboard +
DataGapsSheet para rellenar (abre AddSnapshotView con el mes que falta). Complementa
la interpolación de gráficas: la línea se ve suave pero el usuario sabe que faltan
datos reales.

Feature 2 — Resumen mensual compartible: MonthlySummaryShareView (tarjeta con marca:
valor, variación desde el check-in, racha, mood/rating) renderizada con ImageRenderer
y compartida vía ShareService. Botón en la fila "check-in done" del Dashboard.

Feature 3 — Import con vista previa: ImportPreview + previewImportAsync (dry-run
READ-ONLY, no muta nada) cuenta qué se creará/actualizará usando los mismos checks
de existencia que applyImport. ImportDataView muestra la confirmación antes de
importar. El path real de import (applyImport/importDataAsync) NO se toca.

Localización en los 7 idiomas.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L2p3gUZRNWW388rWFRjiU7

PortfolioJournal/Views/Dashboard/DashboardView.swift

@@ -15,6 +15,10 @@ struct DashboardView: View {
     @State private var sectionConfigs = DashboardLayoutStore.load()
     @AppStorage("showForecast") private var showForecast = true
     @State private var showingQuickUpdate = false
+    @State private var showingDataGaps = false
+    /// Signature of the gap set last dismissed, so re-dismissal sticks until the
+    /// gaps actually change (e.g. the user filled some).
+    @AppStorage("dismissedDataGapsSignature") private var dismissedGapsSignature = ""
     @Environment(\.horizontalSizeClass) private var horizontalSizeClass
 
     init() {
@@ -39,9 +43,11 @@ struct DashboardView: View {
                             VStack(spacing: 16) {
                                 ForEach(visibleSections) { config in
                                     sectionView(for: config)
-                                    if config.id == DashboardSection.monthlyCheckIn.id,
-                                       !viewModel.insights.isEmpty {
-                                        InsightsRow(insights: viewModel.insights)
+                                    if config.id == DashboardSection.monthlyCheckIn.id {
+                                        gapsBanner
+                                        if !viewModel.insights.isEmpty {
+                                            InsightsRow(insights: viewModel.insights)
+                                        }
                                     }
                                 }
                             }
@@ -131,6 +137,12 @@ struct DashboardView: View {
             .sheet(isPresented: $viewModel.showingPaywall) {
                 PaywallView()
             }
+            .sheet(isPresented: $showingDataGaps) {
+                DataGapsSheet(
+                    gaps: viewModel.dataGaps,
+                    sourceProvider: { viewModel.source(withId: $0) }
+                )
+            }
             .onReceive(NotificationCenter.default.publisher(for: .openQuickUpdate)) { _ in
                 showingQuickUpdate = true
             }
@@ -180,6 +192,29 @@ struct DashboardView: View {
         sectionConfigs.filter { $0.isVisible }
     }
 
+    // MARK: - Data Gaps
+
+    /// A stable fingerprint of the current gap set — changes when gaps are
+    /// added or filled, which re-shows a previously dismissed banner.
+    private var currentGapsSignature: String {
+        viewModel.dataGaps.map { $0.id }.sorted().joined(separator: "|")
+    }
+
+    private var shouldShowGapsBanner: Bool {
+        !viewModel.dataGaps.isEmpty && dismissedGapsSignature != currentGapsSignature
+    }
+
+    @ViewBuilder
+    private var gapsBanner: some View {
+        if shouldShowGapsBanner {
+            DataGapsBanner(
+                totalMissingMonths: viewModel.totalMissingMonths,
+                onTap: { showingDataGaps = true },
+                onDismiss: { dismissedGapsSignature = currentGapsSignature }
+            )
+        }
+    }
+
     // MARK: - iPad Layout Helpers
 
     /// Full-width "hero" zones that lead the dashboard, in order.
@@ -224,8 +259,11 @@ struct DashboardView: View {
                 VStack(spacing: 16) {
                     ForEach(iPadLeadSections) { config in
                         sectionView(for: config)
-                        if config.id == DashboardSection.monthlyCheckIn.id, !viewModel.insights.isEmpty {
-                            InsightsRow(insights: viewModel.insights)
+                        if config.id == DashboardSection.monthlyCheckIn.id {
+                            gapsBanner
+                            if !viewModel.insights.isEmpty {
+                                InsightsRow(insights: viewModel.insights)
+                            }
                         }
                     }
 
@@ -285,7 +323,10 @@ struct DashboardView: View {
                     lastUpdated: viewModel.formattedLastUpdate,
                     pendingCount: viewModel.sourcesNeedingUpdate.count,
                     totalSources: viewModel.totalSourceCount,
-                    streak: viewModel.updateStreak
+                    streak: viewModel.updateStreak,
+                    onShareSummary: {
+                        ShareService.shared.shareMonthlySummary(viewModel.monthlySummaryShareData())
+                    }
                 )
             }
         case .momentumStreaks:
@@ -557,6 +598,7 @@ struct MonthlyCheckInCard: View {
     var pendingCount: Int = 0
     var totalSources: Int = 0
     var streak: Int = 0
+    var onShareSummary: (() -> Void)? = nil
     @State private var startDestinationActive = false
     @State private var showingGuidedFlow = false
 
@@ -734,6 +776,15 @@ struct MonthlyCheckInCard: View {
                 .background(Color.orange.opacity(0.12))
                 .clipShape(Capsule())
             }
+            if let onShareSummary {
+                Button(action: onShareSummary) {
+                    Image(systemName: "square.and.arrow.up")
+                        .font(.caption.weight(.semibold))
+                        .foregroundColor(.appPrimary)
+                }
+                .buttonStyle(.plain)
+                .accessibilityLabel(Text("Share monthly summary"))
+            }
             Button {
                 startDestinationActive = true
             } label: {