Share cards compartibles: brand header grande, fecha, Dark/Light (build 83) #35

- Header de marca arriba, grande (logo BrandMark 48px + nombre title2 rounded),
  nunca se corta en Story (9:16 real 360x640, Post 4:5 360x450).
- Héroe = retorno % (privacy/branding-friendly), valor como apoyo.
- Fecha del último check-in bajo el nombre (share_as_of) para dar contexto a
  quien no conoce la app; DashboardViewModel.shareAsOfDate.
- Tema Dark + Light (ShareCardTheme) con selector en el sheet + preview vivo.
- Sparkline real (viewModel.evolutionData), ya se pasaba.
- CTA de descarga + QR con ct=snapshot_share (atribución App Analytics).
- L10n x7 (as_of, theme_dark/light, cta, hero, metrics).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L38583J7AYWCVPevkivscj

PortfolioJournal/Views/Dashboard/DashboardView.swift

@@ -155,7 +155,8 @@ struct DashboardView: View {
                     yearChange: viewModel.portfolioSummary.formattedYearChange,
                     sinceInceptionChange: viewModel.portfolioSummary.formattedAllTimeReturn,
                     sparkline: viewModel.evolutionData.map { NSDecimalNumber(decimal: $0.value).doubleValue },
-                    isPositive: viewModel.latestPortfolioChange.absolute >= 0
+                    isPositive: viewModel.latestPortfolioChange.absolute >= 0,
+                    asOf: viewModel.shareAsOfDate
                 )
             }
             .sheet(isPresented: $showingDataGaps) {