fix(data): normalize a list working dir's trailing separator on write

A list working_dir stored as "C:\Dev\Tests\StaplerTracking\" broke every consumer
that puts it on a Windows command line: argv rules read \" as an escaped quote, so
the token never closes. "Open in terminal" passed wt.exe a starting directory of
C:\Dev\Tests\StaplerTracking" and it failed with 0x8007010b; the same data had
already corrupted the ConPTY list handler's arg list in August.

Paths.TrimTrailingSeparator is now the single helper (replacing the copies in
InteractiveLaunchSpecService and ClaudeHelpLauncher) and ListRepository applies it
on Add/Update, which covers every writer: UI create, repo import, hub UpdateList,
and MCP CreateList/UpdateList. OpenInTerminal also switches to ArgumentList so its
quoting is correct regardless of what's stored.

src/ClaudeDo.Data/Paths.cs

@@ -25,6 +25,22 @@ public static class Paths
         return Path.GetFullPath(expanded);
     }
 
+    /// <summary>
+    /// Strips trailing directory separators off a path bound for a Windows command line. Windows
+    /// argv rules read <c>\"</c> as an escaped quote, so a quoted token ending in '\' never closes
+    /// (<c>"C:\repo\"</c> parses as <c>C:\repo"</c>) and either the path itself or every argument
+    /// after it is corrupted. A bare root ("C:\", "/") is all separator and is returned untouched;
+    /// so is null/blank.
+    /// </summary>
+    public static string? TrimTrailingSeparator(string? path)
+    {
+        if (string.IsNullOrWhiteSpace(path))
+            return path;
+
+        var trimmed = path.TrimEnd(Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar);
+        return trimmed.Length == 0 || trimmed.EndsWith(':') ? path : trimmed;
+    }
+
     /// <summary>~/.todo-app — parent directory for db, logs, config, sandbox, worktrees.</summary>
     public static string AppDataRoot() =>
         Expand("~/.todo-app");