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/Report/WeekReportServiceTests.cs

@@ -27,7 +27,7 @@ public class WeekReportServiceTests : IDisposable
     {
         public int Calls;
         public RunResult Next = new() { ExitCode = 0, ResultMarkdown = "## Bericht" };
-        public Task<RunResult> RunAsync(string args, string prompt, string wd, Func<string, Task> onLine, CancellationToken ct)
+        public Task<RunResult> RunAsync(IReadOnlyList<string> args, string prompt, string wd, Func<string, Task> onLine, CancellationToken ct)
         { Calls++; return Task.FromResult(Next); }
     }