refactor: apply Single Responsibility Principle to Program.cs and ReplLoop.cs

extracted responsibilities from Program.cs (208→46 lines) and ReplLoop.cs (274→174 lines) into focused service classes: HeaderRenderer, SessionManager, ApplicationStartup, ResponseStreamer, SpinnerService, UsageDisplayer, and ContextCompactionService. Each class now has a single, well-defined responsibility, improving testability and maintainability.

SpinnerService.cs

@@ -0,0 +1,100 @@
+using Spectre.Console;
+
+namespace AnchorCli;
+
+/// <summary>
+/// Manages the "thinking" spinner animation during AI response generation.
+/// </summary>
+internal sealed class SpinnerService : IDisposable
+{
+    private readonly object _consoleLock = new();
+    private CancellationTokenSource? _spinnerCts;
+    private Task? _spinnerTask;
+    private bool _showSpinner = true;
+    private bool _disposed;
+
+    /// <summary>
+    /// Starts the spinner animation.
+    /// </summary>
+    public void Start(CancellationToken cancellationToken)
+    {
+        _spinnerCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
+        _showSpinner = true;
+
+        _spinnerTask = Task.Run(async () =>
+        {
+            var frames = Spinner.Known.BouncingBar.Frames;
+            var interval = Spinner.Known.BouncingBar.Interval;
+            int i = 0;
+
+            Console.Write("\x1b[?25l");
+            try
+            {
+                while (!_spinnerCts.Token.IsCancellationRequested)
+                {
+                    lock (_consoleLock)
+                    {
+                        if (_showSpinner && !_spinnerCts.Token.IsCancellationRequested)
+                        {
+                            var frame = frames[i % frames.Count];
+                            Console.Write($"\r\x1b[38;5;69m{frame}\x1b[0m Thinking...");
+                            i++;
+                        }
+                    }
+                    try { await Task.Delay(interval, _spinnerCts.Token); } catch { }
+                }
+            }
+            finally
+            {
+                lock (_consoleLock)
+                {
+                    if (_showSpinner)
+                        Console.Write("\r" + new string(' ', 40) + "\r");
+                    Console.Write("\x1b[?25h");
+                }
+            }
+        });
+    }
+
+    /// <summary>
+    /// Stops the spinner animation and waits for it to complete.
+    /// </summary>
+    public async Task StopAsync()
+    {
+        _spinnerCts?.Cancel();
+        if (_spinnerTask != null)
+        {
+            await Task.WhenAny(_spinnerTask);
+        }
+    }
+
+    /// <summary>
+    /// Pauses the spinner (e.g., during tool execution).
+    /// </summary>
+    public void Pause()
+    {
+        lock (_consoleLock)
+        {
+            _showSpinner = false;
+            Console.Write("\r" + new string(' ', 40) + "\r");
+        }
+    }
+
+    /// <summary>
+    /// Resumes the spinner after being paused.
+    /// </summary>
+    public void Resume()
+    {
+        lock (_consoleLock)
+        {
+            _showSpinner = true;
+        }
+    }
+
+    public void Dispose()
+    {
+        if (_disposed) return;
+        _spinnerCts?.Dispose();
+        _disposed = true;
+    }
+}