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/Prime/DailyPrepPrompt.cs

@@ -5,6 +5,9 @@ public static class DailyPrepPrompt
     public const string CandidatesTool = "mcp__claudedo__get_daily_prep_candidates";
     public const string SetMyDayTool = "mcp__claudedo__set_my_day";
 
+    public static string LogPath() =>
+        System.IO.Path.Combine(ClaudeDo.Data.Paths.AppDataRoot(), "logs", "daily-prep.log");
+
     public static string BuildArgs(int maxTurns) =>
         "-p --output-format stream-json --verbose --permission-mode acceptEdits " +
         $"--max-turns {maxTurns} " +