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.Data/Configuration/TaskEntityConfiguration.cs

@@ -78,6 +78,9 @@ public class TaskEntityConfiguration : IEntityTypeConfiguration<TaskEntity>
         builder.Property(t => t.Result).HasColumnName("result");
         builder.Property(t => t.ReviewFeedback).HasColumnName("review_feedback");
         builder.Property(t => t.RoadblockCount).HasColumnName("roadblock_count").HasDefaultValue(0);
+        builder.Property(t => t.FailureReason).HasColumnName("failure_reason");
+        builder.Property(t => t.FailureTurnsUsed).HasColumnName("failure_turns_used");
+        builder.Property(t => t.FailureMaxTurns).HasColumnName("failure_max_turns");
         builder.Property(t => t.LogPath).HasColumnName("log_path");
         builder.Property(t => t.CreatedAt).HasColumnName("created_at").IsRequired();
         builder.Property(t => t.StartedAt).HasColumnName("started_at");