[EPAC-1978]: switch sheets to adaptive form presentation

ios/epac/DesignSystem/Modifiers/AdaptiveLayout.swift

@@ -50,6 +50,44 @@ private struct RegularSizeClassItemFormSheetModifier<Item: Identifiable, SheetCo
     }
 }
 
+private struct FormSheetPresentationConfigurator: UIViewControllerRepresentable {
+    func makeUIViewController(context: Context) -> Controller {
+        Controller()
+    }
+
+    func updateUIViewController(_ uiViewController: Controller, context: Context) {
+        uiViewController.applyFormSheetPresentation()
+    }
+
+    final class Controller: UIViewController {
+        override func didMove(toParent parent: UIViewController?) {
+            super.didMove(toParent: parent)
+            applyFormSheetPresentation()
+        }
+
+        override func viewWillAppear(_ animated: Bool) {
+            super.viewWillAppear(animated)
+            applyFormSheetPresentation()
+        }
+
+        func applyFormSheetPresentation() {
+            guard let presentationHost else { return }
+            presentationHost.modalPresentationStyle = .formSheet
+        }
+
+        private var presentationHost: UIViewController? {
+            var controller = parent
+            while let current = controller {
+                if current.presentingViewController != nil {
+                    return current
+                }
+                controller = current.parent
+            }
+            return parent
+        }
+    }
+}
+
 extension View {
     /// Constrains long-form reading surfaces to `AdaptiveLayout.readingWidth` in a regular
     /// horizontal size class while leaving compact layouts unchanged.
@@ -63,8 +101,8 @@ extension View {
         modifier(AdaptiveReadingWidthModifier())
     }
 
-    /// Presents a sheet normally in compact width and with medium/large detents plus a visible
-    /// drag indicator in a regular horizontal size class.
+    /// Presents a sheet normally in compact width and as a form-sized sheet with medium/large
+    /// detents plus a visible drag indicator in a regular horizontal size class.
     ///
     /// Use this as the Stage-2 drop-in replacement for `.sheet(isPresented:content:)` when a
     /// modal should adapt to iPad and Mac Catalyst form-sheet ergonomics. Do not use it for flows
@@ -76,8 +114,8 @@ extension View {
         regularSizeClassFormSheet(isPresented: isPresented, onDismiss: nil, content: content)
     }
 
-    /// Presents a sheet normally in compact width and with medium/large detents plus a visible
-    /// drag indicator in a regular horizontal size class.
+    /// Presents a sheet normally in compact width and as a form-sized sheet with medium/large
+    /// detents plus a visible drag indicator in a regular horizontal size class.
     ///
     /// Use this as the Stage-2 drop-in replacement for `.sheet(isPresented:onDismiss:content:)`
     /// when a modal should adapt to iPad and Mac Catalyst form-sheet ergonomics. Do not use it for
@@ -96,8 +134,8 @@ extension View {
         )
     }
 
-    /// Presents an item-driven sheet normally in compact width and with medium/large detents plus
-    /// a visible drag indicator in a regular horizontal size class.
+    /// Presents an item-driven sheet normally in compact width and as a form-sized sheet with
+    /// medium/large detents plus a visible drag indicator in a regular horizontal size class.
     ///
     /// Use this as the Stage-2 drop-in replacement for `.sheet(item:onDismiss:content:)` when a
     /// modal should adapt to iPad and Mac Catalyst form-sheet ergonomics. Do not use it for flows
@@ -121,8 +159,15 @@ private extension View {
     @ViewBuilder
     func regularSizeClassSheetChrome(isEnabled: Bool) -> some View {
         if isEnabled {
-            presentationDetents([.medium, .large])
-                .presentationDragIndicator(.visible)
+            if #available(iOS 18.0, *) {
+                presentationSizing(.form)
+                    .presentationDetents([.medium, .large])
+                    .presentationDragIndicator(.visible)
+            } else {
+                background(FormSheetPresentationConfigurator())
+                    .presentationDetents([.medium, .large])
+                    .presentationDragIndicator(.visible)
+            }
         } else {
             self
         }

ios/epac/Views/Common/DataSourceBadge.swift

@@ -48,7 +48,7 @@ struct DataSourceBadge: View {
         }
         .accessibilityLabel("\(source.name) — \(badgeText)")
         .accessibilityHint("Opens source details")
-        .sheet(isPresented: $showDetail) {
+        .regularSizeClassFormSheet(isPresented: $showDetail) {
             DataSourceDetailSheet(source: source)
         }
     }

ios/epac/Views/Common/ExplainerCard.swift

@@ -121,7 +121,7 @@ struct ExplainerTipModifier: ViewModifier {
                 .buttonStyle(.plain)
                 .accessibilityLabel("What is \(term)?")
             }
-            .sheet(isPresented: $showExplainer) {
+            .regularSizeClassFormSheet(isPresented: $showExplainer) {
                 ExplainerCard(explainer: explainer)
             }
         } else {

ios/epac/Views/ContentView.swift

@@ -146,7 +146,7 @@ struct ContentView: View {
 			}
 			.interactiveDismissDisabled()
 		}
-		.sheet(isPresented: $showMyMPSetup) {
+		.regularSizeClassFormSheet(isPresented: $showMyMPSetup) {
 			PostalCodeSetupView { showMyMPSetup = false }
 		}
 		.onChange(of: router.pendingShowPostalCodeSetup) { _, pending in
@@ -160,7 +160,7 @@ struct ContentView: View {
 			handleQuickAction(action)
 			router.pendingQuickAction = nil
 		}
-		.sheet(isPresented: $showWhatsNew) {
+		.regularSizeClassFormSheet(isPresented: $showWhatsNew) {
 			WhatsNewView { showWhatsNew = false }
 				.presentationDetents([.medium])
 				.presentationDragIndicator(.visible)

ios/epac/Views/Home/HomeFeedView.swift

@@ -129,13 +129,13 @@ struct HomeFeedView: View {
             .task {
                 await loadFeed()
             }
-            .sheet(isPresented: $showPostalCodeSetup) {
+            .regularSizeClassFormSheet(isPresented: $showPostalCodeSetup) {
                 PostalCodeSetupView { showPostalCodeSetup = false }
             }
             .onChange(of: postalCodeStore.savedMemberName) {
                 Task { await loadFeed() }
             }
-            .sheet(isPresented: $showSettings) {
+            .regularSizeClassFormSheet(isPresented: $showSettings) {
                 SettingsView()
             }
         }

ios/epac/Views/Members/MemberProfileView.swift

@@ -427,7 +427,7 @@ struct MemberProfileView: View {
 				.environmentObject(fetch)
 		}
 		.activitySheet($shareItem)
-		.sheet(isPresented: $showingComparePicker) {
+		.regularSizeClassFormSheet(isPresented: $showingComparePicker) {
 			NavigationStack {
 				List(pickableMembers) { other in
 					Button {

ios/epac/Views/Members/PartyLineScoreView.swift

@@ -50,7 +50,7 @@ struct PartyLineScoreView: View {
         .padding()
         .background(Color(.secondarySystemBackground))
         .cornerRadius(EpacCornerRadius.m)
-        .sheet(isPresented: $showInfo) { infoSheet }
+        .regularSizeClassFormSheet(isPresented: $showInfo) { infoSheet }
     }
 
     private var infoSheet: some View {

ios/epac/Views/MyMP/MyMPView.swift

@@ -178,7 +178,7 @@ struct MyMPView: View {
                 Task { await loadActivities() }
             }
         }
-        .sheet(isPresented: $showPostalCodeSetup) {
+        .regularSizeClassFormSheet(isPresented: $showPostalCodeSetup) {
             PostalCodeSetupView { showPostalCodeSetup = false }
         }
     }

ios/epac/Views/Settings/SettingsView.swift

@@ -36,7 +36,7 @@ struct SettingsView: View {
                     Button(NSLocalizedString("settings.done", comment: "")) { dismiss() }
                 }
             }
-            .sheet(isPresented: $showPostalCodeChange) {
+            .regularSizeClassFormSheet(isPresented: $showPostalCodeChange) {
                 PostalCodeSetupView { showPostalCodeChange = false }
             }
         }