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>

tests/ClaudeDo.Worker.Tests/State/TaskStateServiceTests.cs

@@ -243,6 +243,17 @@ public sealed class TaskStateServiceTests : IDisposable
         Assert.Equal(TaskStatus.Done, await GetStatusAsync(id));
     }
 
+    [Fact]
+    public async Task FailAsync_FromWaitingForReview_IsNoOp()
+    {
+        var id = await SeedTaskAsync(TaskStatus.WaitingForReview);
+
+        var result = await _sut.FailAsync(id, DateTime.UtcNow, "oops", default);
+
+        Assert.False(result.Ok);
+        Assert.Equal(TaskStatus.WaitingForReview, await GetStatusAsync(id));
+    }
+
     // ─── CancelAsync ──────────────────────────────────────────────────────
 
     [Fact]