STATE-WP-0070 T04 (partial): drop open_workstreams from /state/summary

Removes the redundant open_workstreams mirror field from StateSummary (schema,
router, MCP get_domain_summary reader, dashboard consumers + empty-state stub,
and tests). Consumers already preferred open_workplans, so this is the
low-risk half of T04.

Deferred (still have live callers — not yet retirement-ready):
- workstream_id query/body field alias on preferred routes — external
  session-close curls/scripts fleet-wide still send it.
- flows/workstream.yaml — /flows/workstream/{id} routes are still served and
  exercised by tests; retire only once no callers remain.

Staged on branch state-wp-0070-legacy-retirement — do not merge until the 7th
documented zero-usage window is captured.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

dashboard/src/data/summary.json.py

@@ -38,5 +38,4 @@ except urllib.error.URLError as e:
         "blocked_tasks": [],
         "recent_progress": [],
         "open_workplans": [],
-        "open_workstreams": [],
     }))

dashboard/src/index.md

@@ -437,7 +437,7 @@ display(html`<div class="grid grid-cols-3" style="gap:1rem;margin-bottom:1.5rem"
 
 ```js
 const waitingTasks = summary.waiting_tasks ?? summary.blocked_tasks ?? [];
-const wsById = Object.fromEntries((summary.open_workplans ?? summary.open_workstreams ?? []).map(w => [w.id, w]));
+const wsById = Object.fromEntries((summary.open_workplans ?? []).map(w => [w.id, w]));
 const todayCount = (summary.recent_progress ?? []).filter(e =>
   e.created_at?.startsWith(new Date().toISOString().slice(0, 10))).length;
 const decCount = (decisions.open ?? 0) + (decisions.escalated ?? 0);