fix(mcp): report a Failed task's failureReason instead of a bare status

get_task/batch_get_tasks now return failureReason (max_turns|timeout|error|
cancelled|unknown) plus failureTurnsUsed/failureMaxTurns on a Failed task, so
max_turns (worktree usually fine, continue_task) is distinguishable from a
real error (reset_failed_task) without pulling get_task_log's raw NDJSON.
Classified and stamped onto TaskEntity by TaskRunner.MarkFailed via
TaskStateService.FailAsync; TaskRunEntity also keeps the CLI's raw
terminal_reason/result_subtype/errors for deeper diagnosis. reset_failed_task's
description now warns explicitly that it discards the worktree and points at
continue_task for max_turns. Surfaced on the task card's status-chip tooltip.

src/ClaudeDo.Worker/State/Interfaces/ITaskStateService.cs

@@ -8,7 +8,9 @@ public interface ITaskStateService
     Task<TransitionResult> SubmitForReviewAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct);
     Task<TransitionResult> SubmitInteractiveForReviewAsync(string taskId, DateTime finishedAt, CancellationToken ct);
     Task<TransitionResult> SubmitForChildrenAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct);
-    Task<TransitionResult> FailAsync(string taskId, DateTime finishedAt, string? error, CancellationToken ct);
+    Task<TransitionResult> FailAsync(
+        string taskId, DateTime finishedAt, string? error, CancellationToken ct,
+        string failureReason = "error", int? turnsUsed = null, int? maxTurns = null);
     Task<TransitionResult> CancelAsync(string taskId, DateTime finishedAt, CancellationToken ct, bool allowFromIdle = false);
     Task<TransitionResult> ResetToIdleAsync(string taskId, CancellationToken ct);