feat(daily-prep): persist last prep run to a log file and serve it via GetLastPrepLog

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.Worker/Hub/WorkerHub.cs

@@ -582,6 +582,19 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         await new DailyNoteRepository(ctx).DeleteAsync(id);
     }
 
+    public Task<string> GetLastPrepLog()
+    {
+        var path = DailyPrepPrompt.LogPath();
+        if (!File.Exists(path)) return Task.FromResult(string.Empty);
+
+        const int maxBytes = 256 * 1024;
+        var bytes = File.ReadAllBytes(path);
+        var text = bytes.Length <= maxBytes
+            ? System.Text.Encoding.UTF8.GetString(bytes)
+            : System.Text.Encoding.UTF8.GetString(bytes, bytes.Length - maxBytes, maxBytes);
+        return Task.FromResult(text);
+    }
+
     public async Task<int> ClearMyDay()
     {
         await using var ctx = await _dbFactory.CreateDbContextAsync();