fix(worker): harden CLI injection, stuck-Running, chain wedge, and Fail guard

1. ArgumentList (fix injection): ClaudeArgsBuilder.Build() now returns
   IReadOnlyList<string>; ClaudeProcess populates ProcessStartInfo.ArgumentList
   instead of Arguments, so values like system prompts are never shell-split.
   DailyPrepPrompt, RefinePrompt, and WeekReportService migrated similarly.
   All IClaudeProcess fakes updated.

2. ContinueAsync exception guard: wrap RunOnceAsync in try/catch matching
   the RunAsync pattern so an unexpected exception never leaves the task
   stuck in Running status.

3. Planning chain cascade: OnChildFinishedAsync now calls CancelAsync on
   the immediate blocked successor when a child fails or is cancelled,
   triggering a recursive cascade that clears the entire remaining chain
   instead of leaving it wedged.

4. FailAsync guard: restrict valid source states to Running and Queued;
   WaitingForReview -> Failed is now rejected, preventing an invalid
   transition that could corrupt the review workflow.

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

src/ClaudeDo.Worker/State/TaskStateService.cs

@@ -196,14 +196,15 @@ public sealed class TaskStateService : ITaskStateService
         await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
         {
             var affected = await ctx.Tasks
-                .Where(t => t.Id == taskId && t.Status != TaskStatus.Done)
+                .Where(t => t.Id == taskId &&
+                    (t.Status == TaskStatus.Running || t.Status == TaskStatus.Queued))
                 .ExecuteUpdateAsync(s => s
                     .SetProperty(t => t.Status, TaskStatus.Failed)
                     .SetProperty(t => t.FinishedAt, finishedAt)
                     .SetProperty(t => t.Result, error), ct);
 
             if (affected == 0)
-                return new TransitionResult(false, "Task already done; cannot fail.");
+                return new TransitionResult(false, "Task not in a failable state (must be Running or Queued).");
         }
 
         await OnChildTerminalAsync(taskId, TaskStatus.Failed);