feat: add theme and high-density display modes

Refs: https://todo.sr.ht/~ccleberg/hutch/24
Implements: https://todo.sr.ht/~ccleberg/hutch/25

3 files changed, 83 insertions, 0 deletions

diff --git a/Hutch/App/AppStorageKeys.swift b/Hutch/App/AppStorageKeys.swift
index ff309d4..eaf54f0 100644
--- a/Hutch/App/AppStorageKeys.swift
+++ b/Hutch/App/AppStorageKeys.swift
@@ -13,4 +13,6 @@ enum AppStorageKeys {
     static let homeBuildsExpanded = "homeBuildsExpanded"
     static let buildsAutoRefreshInterval = "buildsAutoRefreshInterval"
     static let buildsRepoFilter = "buildsRepoFilter"
+    static let appTheme = "appTheme"
+    static let displayDensity = "displayDensity"
 }
diff --git a/Hutch/App/HutchApp.swift b/Hutch/App/HutchApp.swift
index e65833c..016ddd0 100644
--- a/Hutch/App/HutchApp.swift
+++ b/Hutch/App/HutchApp.swift
@@ -4,12 +4,17 @@ import SwiftUI
 struct HutchApp: App {
     @State private var appState = AppState()
     @State private var networkMonitor = NetworkMonitor()
+    @AppStorage(AppStorageKeys.appTheme) private var appTheme: AppTheme = .system
+    @AppStorage(AppStorageKeys.displayDensity) private var displayDensity: DisplayDensity = .standard
 
     var body: some Scene {
         WindowGroup {
             RootView()
                 .environment(appState)
                 .environment(networkMonitor)
+                .environment(\.displayDensity, displayDensity)
+                .environment(\.defaultMinListRowHeight, displayDensity == .compact ? 36 : 44)
+                .preferredColorScheme(appTheme.colorScheme)
                 .onOpenURL { url in
                     if let link = DeepLink(url: url) {
                         appState.pendingDeepLink = link
diff --git a/Hutch/App/ThemeManager.swift b/Hutch/App/ThemeManager.swift
new file mode 100644
index 0000000..ee74921
--- /dev/null
+++ b/Hutch/App/ThemeManager.swift
@@ -0,0 +1,76 @@
+import SwiftUI
+
+// MARK: - Theme & Density Types
+
+enum AppTheme: String, CaseIterable, Identifiable {
+    case system
+    case light
+    case dark
+
+    var id: String { rawValue }
+
+    var label: String {
+        switch self {
+        case .system: "System"
+        case .light: "Light"
+        case .dark: "Dark"
+        }
+    }
+
+    var colorScheme: ColorScheme? {
+        switch self {
+        case .system: nil
+        case .light: .light
+        case .dark: .dark
+        }
+    }
+}
+
+enum DisplayDensity: String, CaseIterable, Identifiable {
+    case standard
+    case compact
+
+    var id: String { rawValue }
+
+    var label: String {
+        switch self {
+        case .standard: "Standard"
+        case .compact: "Compact"
+        }
+    }
+}
+
+// MARK: - Environment Keys
+
+private struct DisplayDensityKey: EnvironmentKey {
+    static let defaultValue: DisplayDensity = .standard
+}
+
+extension EnvironmentValues {
+    var displayDensity: DisplayDensity {
+        get { self[DisplayDensityKey.self] }
+        set { self[DisplayDensityKey.self] = newValue }
+    }
+}
+
+// MARK: - Themed List Modifier
+
+/// Combined modifier for List/Form that applies compact section spacing.
+/// Apply once per List or Form.
+struct ThemedListStyle: ViewModifier {
+    @Environment(\.displayDensity) private var density
+
+    func body(content: Content) -> some View {
+        content
+            .listSectionSpacing(density == .compact ? .compact : .default)
+            .contentMargins(.vertical, density == .compact ? 2 : 8, for: .scrollContent)
+            .controlSize(density == .compact ? .small : .regular)
+    }
+}
+
+extension View {
+    /// Apply themed appearance (density spacing) to a List or Form.
+    func themedList() -> some View {
+        modifier(ThemedListStyle())
+    }
+}