Add themes selector

Downterm/CommandNotch/AppDelegate.swift

@@ -19,6 +19,7 @@ class AppDelegate: NSObject, NSApplicationDelegate {
         observeDisplayPreference()
         observeSizePreferences()
         observeFontSizeChanges()
+        observeTerminalThemeChanges()
     }
 
     func applicationWillTerminate(_ notification: Notification) {
@@ -58,6 +59,16 @@ class AppDelegate: NSObject, NSApplicationDelegate {
             }
             .store(in: &cancellables)
     }
+
+    /// Live-update terminal colors across all sessions.
+    private func observeTerminalThemeChanges() {
+        UserDefaults.standard.publisher(for: \.terminalTheme)
+            .removeDuplicates()
+            .sink { newTheme in
+                TerminalManager.shared.updateAllThemes(TerminalTheme.resolve(newTheme))
+            }
+            .store(in: &cancellables)
+    }
 }
 
 // MARK: - KVO key paths
@@ -67,6 +78,10 @@ private extension UserDefaults {
         double(forKey: NotchSettings.Keys.terminalFontSize)
     }
 
+    @objc var terminalTheme: String {
+        string(forKey: NotchSettings.Keys.terminalTheme) ?? NotchSettings.Defaults.terminalTheme
+    }
+
     @objc var showOnAllDisplays: Bool {
         bool(forKey: NotchSettings.Keys.showOnAllDisplays)
     }