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/Prime/DailyPrepPrompt.cs

@@ -8,10 +8,13 @@ public static class DailyPrepPrompt
     public static string LogPath() =>
         System.IO.Path.Combine(ClaudeDo.Data.Paths.AppDataRoot(), "logs", "daily-prep.log");
 
-    public static string BuildArgs(int maxTurns) =>
-        "-p --output-format stream-json --verbose --permission-mode acceptEdits " +
-        $"--max-turns {maxTurns} " +
-        $"--allowedTools {CandidatesTool} {SetMyDayTool}";
+    public static IReadOnlyList<string> BuildArgs(int maxTurns) =>
+    [
+        "-p", "--output-format", "stream-json", "--verbose",
+        "--permission-mode", "acceptEdits",
+        "--max-turns", maxTurns.ToString(),
+        "--allowedTools", CandidatesTool, SetMyDayTool,
+    ];
 
     public static string BuildPrompt(int maxTasks, DateOnly today) =>
         ClaudeDo.Data.PromptFiles.Render(