feat(worker): surface task numbers in MCP tool return payloads

Adds Number alongside every task id in External/'s DTOs -- the two
central mappers (ToDto/ToRefDto -> TaskDto/TaskRefDto) plus every
DTO that carries a bare task id and bypasses them (batch results,
queue state, wait-for-change, config, attachments, handoff,
lifecycle, merge-preview-set, worktree list). Input resolution
(#123 as an argument) stays for slice 3.

src/ClaudeDo.Worker/Worktrees/WorktreeMaintenanceService.cs

@@ -91,7 +91,7 @@ public sealed class WorktreeMaintenanceService
                     join l in context.Lists on t.ListId equals l.Id
                     select new
                     {
-                        w.TaskId, t.Title, t.Status, ListId = l.Id, ListName = l.Name,
+                        w.TaskId, t.Number, t.Title, t.Status, ListId = l.Id, ListName = l.Name,
                         w.Path, w.BranchName, w.BaseCommit, w.State, w.DiffStat, w.CreatedAt,
                     };
 
@@ -101,7 +101,7 @@ public sealed class WorktreeMaintenanceService
         var rows = await query.AsNoTracking().ToListAsync(ct);
 
         return rows.Select(x => new WorktreeOverviewRow(
-            x.TaskId, x.Title, x.Status, x.ListId, x.ListName,
+            x.TaskId, x.Number, x.Title, x.Status, x.ListId, x.ListName,
             x.Path, x.BranchName, x.BaseCommit ?? "", x.State, x.DiffStat, x.CreatedAt,
             PathExistsOnDisk: !string.IsNullOrWhiteSpace(x.Path) && Directory.Exists(x.Path))).ToList();
     }