Add debug logging with Show Log button

- DebugLogger class saves logs to %TEMP%\CMM\debug.log
- Show Log button appears after 3s if loading takes too long
- Log viewer with Copy to Clipboard and Open Log File options
- Detailed logging throughout LoadMonitors for debugging

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

DellMonitorControl/DebugLogger.cs

@@ -0,0 +1,77 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+
+namespace DellMonitorControl;
+
+public static class DebugLogger
+{
+    private static readonly List<string> _logs = new();
+    private static readonly object _lock = new();
+    private static readonly string _logFilePath;
+
+    static DebugLogger()
+    {
+        var tempPath = Path.Combine(Path.GetTempPath(), "CMM");
+        Directory.CreateDirectory(tempPath);
+        _logFilePath = Path.Combine(tempPath, "debug.log");
+    }
+
+    public static void Log(string message)
+    {
+        var entry = $"[{DateTime.Now:HH:mm:ss.fff}] {message}";
+        lock (_lock)
+        {
+            _logs.Add(entry);
+            try
+            {
+                File.AppendAllText(_logFilePath, entry + Environment.NewLine);
+            }
+            catch { }
+        }
+    }
+
+    public static void LogError(string message, Exception? ex = null)
+    {
+        var entry = ex != null
+            ? $"[{DateTime.Now:HH:mm:ss.fff}] ERROR: {message} - {ex.GetType().Name}: {ex.Message}"
+            : $"[{DateTime.Now:HH:mm:ss.fff}] ERROR: {message}";
+        lock (_lock)
+        {
+            _logs.Add(entry);
+            if (ex != null)
+                _logs.Add($"    Stack: {ex.StackTrace}");
+            try
+            {
+                File.AppendAllText(_logFilePath, entry + Environment.NewLine);
+                if (ex != null)
+                    File.AppendAllText(_logFilePath, $"    Stack: {ex.StackTrace}" + Environment.NewLine);
+            }
+            catch { }
+        }
+    }
+
+    public static string GetLogs()
+    {
+        lock (_lock)
+        {
+            return string.Join(Environment.NewLine, _logs);
+        }
+    }
+
+    public static void Clear()
+    {
+        lock (_lock)
+        {
+            _logs.Clear();
+            try
+            {
+                File.WriteAllText(_logFilePath, "");
+            }
+            catch { }
+        }
+    }
+
+    public static string LogFilePath => _logFilePath;
+}