Add lead workflows, PDF signing, AR projects and photo gallery integration

GasTankAR/Views/Leads/Detail/LeadARProjectsSheet.swift

@@ -0,0 +1,47 @@
+import SwiftUI
+import SwiftData
+
+/// Composition boundary: the AR picker receives only neutral project data.
+struct LeadARProjectsSheet: View {
+    let detail: LeadDetail
+    @Environment(\.modelContext) private var context
+    @State private var service: LeadARProjectsService?
+
+    var body: some View {
+        Group {
+            if let service {
+                LeadARProjectsContent(service: service)
+            } else {
+                ProgressView()
+            }
+        }
+        .task {
+            if service == nil {
+                service = LeadARProjectsService(detail: detail, container: context.container)
+            }
+        }
+    }
+}
+
+private struct LeadARProjectsContent: View {
+    let service: LeadARProjectsService
+    @State private var activeProject: Project?
+    @State private var errorMessage: String?
+
+    var body: some View {
+        ARProjectsSheet(service: service) { id in
+            do { activeProject = try service.resolveProject(id: id) }
+            catch { errorMessage = error.localizedDescription }
+        }
+        .fullScreenCover(item: $activeProject) { project in
+            if let context = project.modelContext {
+                ARExperienceView(project: project).modelContext(context)
+            }
+        }
+        .alert("AR-Projekt konnte nicht geöffnet werden",
+               isPresented: Binding(get: { errorMessage != nil },
+                                    set: { if !$0 { errorMessage = nil } })) {
+            Button("OK", role: .cancel) { errorMessage = nil }
+        } message: { Text(errorMessage ?? "") }
+    }
+}