Add per-workstream task counts to state summary and dashboard

API:
- WorkstreamWithTaskCounts schema extends WorkstreamRead with
  tasks_total/todo/in_progress/blocked/done fields
- /state/summary now includes these counts in open_workstreams via
  a single extra GROUP BY query (workstream_id, status)

Dashboard:
- Replace domain workstream-count bar with a horizontal stacked
  progress bar per workstream (done/in-progress/blocked/todo)
- Workstreams with no tasks show "no tasks yet" annotation
- Workstreams with tasks show "X/N done" label after the bar
- Sorted by domain then title so domains group naturally

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/schemas/workstream.py

@@ -36,3 +36,11 @@ class WorkstreamRead(BaseModel):
     due_date: date | None = None
     created_at: datetime
     updated_at: datetime
+
+
+class WorkstreamWithTaskCounts(WorkstreamRead):
+    tasks_total: int = 0
+    tasks_todo: int = 0
+    tasks_in_progress: int = 0
+    tasks_blocked: int = 0
+    tasks_done: int = 0