Add solar charge controller integration and firmware

App:
- New DeviceRole.solar with its own BLE session/protocol/state
  (SolarSession, VanAlignSolarProtocol, SolarState), mirroring the
  leveling sensor but deliberately not wired into the Live Activity.
- BluetoothManager now keeps an in-memory history per metric (voltage,
  current, power) instead of a single primary-metric series; cleared on
  app restart by design, not persisted to disk.
- DeviceDetailView shows a channel picker above the history chart when a
  device has more than one chartable metric.
- AddDeviceView recognizes the solar service UUID during setup.
- DemoData gets a simulated solar device so the integration can be
  checked in the simulator without hardware.

Firmware:
- Add esp32_ble_solar.yaml (Votronic solar charge controller over BLE)
  and simulated variants (esp32_ble_sim.yaml, esp32_ble_solar_sim.yaml)
  for testing without a vehicle.
- esp32_ble.yaml: set flash_size/psram for the ESP32-S3 N16R8 module.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CamperMonitor/Views/DeviceDetailView.swift

@@ -35,9 +35,31 @@ struct DeviceDetailView: View {
         store.devices.first { $0.id == device.id } ?? device
     }
 
+    /// Nur solange die App läuft: siehe `DeviceHistory`.
+    @State private var selectedHistoryMetricKey: String?
+
     private var snapshot: DeviceSnapshot? { bluetooth.snapshots[device.id] }
     private var linkState: DeviceLinkState { bluetooth.linkStates[device.id] ?? .searching }
-    private var samples: [HistorySample] { bluetooth.history[device.id] ?? [] }
+    private var deviceHistory: DeviceHistory { bluetooth.history[device.id] ?? [:] }
+
+    /// Nur Metriken, zu denen sich bereits ein Verlauf mit mehr als einem
+    /// Punkt angesammelt hat – sonst gäbe es nichts zu zeichnen.
+    private var chartableMetrics: [Metric] {
+        (snapshot?.metrics ?? []).filter { (deviceHistory[$0.key]?.count ?? 0) > 1 }
+    }
+
+    private var selectedMetric: Metric? {
+        if let key = selectedHistoryMetricKey,
+           let metric = chartableMetrics.first(where: { $0.key == key }) {
+            return metric
+        }
+        return chartableMetrics.first(where: \.isPrimary) ?? chartableMetrics.first
+    }
+
+    private var samples: [HistorySample] {
+        guard let selectedMetric else { return [] }
+        return deviceHistory[selectedMetric.key] ?? []
+    }
 
     var body: some View {
         List {
@@ -65,20 +87,38 @@ struct DeviceDetailView: View {
                 }
             }
 
-            if samples.count > 1, let primary = snapshot?.primaryMetric {
-                Section("Verlauf – \(primary.label)") {
+            if let metric = selectedMetric, samples.count > 1 {
+                Section {
+                    if chartableMetrics.count > 1 {
+                        Picker("Messgrösse", selection: Binding(
+                            get: { metric.key },
+                            set: { selectedHistoryMetricKey = $0 }
+                        )) {
+                            ForEach(chartableMetrics) { candidate in
+                                Text(candidate.label).tag(candidate.key)
+                            }
+                        }
+                        .pickerStyle(.segmented)
+                        .listRowInsets(EdgeInsets())
+                        .padding(.horizontal)
+                        .padding(.top, 4)
+                    }
                     Chart(samples) { sample in
                         AreaMark(x: .value("Zeit", sample.time),
-                                 y: .value(primary.label, sample.value))
+                                 y: .value(metric.label, sample.value))
                         .foregroundStyle(.tint.opacity(0.15))
                         LineMark(x: .value("Zeit", sample.time),
-                                 y: .value(primary.label, sample.value))
+                                 y: .value(metric.label, sample.value))
                         .foregroundStyle(.tint)
                         .interpolationMethod(.monotone)
                     }
-                    .chartYAxisLabel(primary.unit)
+                    .chartYAxisLabel(metric.unit)
                     .frame(height: 180)
                     .padding(.vertical, 8)
+                } header: {
+                    Text("Verlauf – \(metric.label)")
+                } footer: {
+                    Text("Nur für die laufende Sitzung – wird beim Neustart der App verworfen.")
                 }
             }