Add tank catalog with USDZ models and tank selection

Introduce TankDefinition/TankCatalog loaded from Tanks.json, bundle the
Drachengas USDZ tank models, add tank selection and preview views, and
update the AR experience, editor and project views to use the catalog.
Includes tests for catalog loading and model selection.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

GasTankAR/Views/ProjectCreate.swift

@@ -12,6 +12,8 @@ struct ProjectCreateView: View {
     @Environment(\.modelContext) private var modelContext
     @Environment(\.dismiss) private var dismiss
 
+    let onCreated: (Project) -> Void
+
     @State private var leadID: String = ""
     @State private var customerName: String = ""
     @State private var creationDate: Date = .now
@@ -41,9 +43,7 @@ struct ProjectCreateView: View {
                     )
                 }
 
-                Section("Tankauswahl") {
-                    TankEditor(tank: $tank)
-                }
+                TankSelectionSection(tank: $tank)
             }
             .navigationTitle("Projekt erstellen")
             .navigationBarTitleDisplayMode(.inline)
@@ -72,11 +72,12 @@ struct ProjectCreateView: View {
             tank: tank
         )
         modelContext.insert(project)
+        onCreated(project)
         dismiss()
     }
 }
 
 #Preview {
-    ProjectCreateView()
+    ProjectCreateView { _ in }
         .modelContainer(for: Project.self, inMemory: true)
 }