Refactor: Reorganize project structure by moving core components into dedicated directories and introducing new configuration and API models.

Core/StateTracker.cs

@@ -0,0 +1,37 @@
+namespace Toak.Core;
+
+public static class StateTracker
+{
+    private static readonly string StateFilePath = Path.Combine(Path.GetTempPath(), "toak_state.pid");
+
+    public static bool IsRecording()
+    {
+        return File.Exists(StateFilePath);
+    }
+
+    public static void SetRecording(int ffmpegPid)
+    {
+        File.WriteAllText(StateFilePath, ffmpegPid.ToString());
+    }
+
+    public static int? GetRecordingPid()
+    {
+        if (File.Exists(StateFilePath))
+        {
+            var content = File.ReadAllText(StateFilePath).Trim();
+            if (int.TryParse(content, out var pid))
+            {
+                return pid;
+            }
+        }
+        return null;
+    }
+
+    public static void ClearRecording()
+    {
+        if (File.Exists(StateFilePath))
+        {
+            File.Delete(StateFilePath);
+        }
+    }
+}