Add Outlook folder browser and user settings

- Replace Outlook folder ComboBox with TextBox + Browse button
  that opens a TreeView-based folder browser dialog
- Add per-user settings stored in %AppData% (not HKLM)
  with option to start minimized (System Tray only)
- Add Settings button to main window
- Settings are per-user, independent of profiles

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/StarfaceOutlookSync/Models/UserSettings.cs

@@ -0,0 +1,37 @@
+using System;
+using System.IO;
+using Newtonsoft.Json;
+
+namespace StarfaceOutlookSync.Models
+{
+    public class UserSettings
+    {
+        public bool StartMinimized { get; set; } = false;
+
+        private static readonly string SettingsFile = Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
+            "StarfaceOutlookSync", "settings.json");
+
+        public static UserSettings Load()
+        {
+            try
+            {
+                if (File.Exists(SettingsFile))
+                    return JsonConvert.DeserializeObject<UserSettings>(File.ReadAllText(SettingsFile))
+                           ?? new UserSettings();
+            }
+            catch { }
+            return new UserSettings();
+        }
+
+        public void Save()
+        {
+            try
+            {
+                Directory.CreateDirectory(Path.GetDirectoryName(SettingsFile));
+                File.WriteAllText(SettingsFile, JsonConvert.SerializeObject(this, Formatting.Indented));
+            }
+            catch { }
+        }
+    }
+}