Migrate remaining in-repo workstream REST callers to /workplans

Point cleanup_stale_tasks, validate_repo_adr, custodian_cli, dashboard data
loaders, extensions poll, MCP legacy resource, and consistency_check task
queries at preferred /workplans routes. Add caller inventory evidence doc.

mcp_server/server.py

@@ -276,7 +276,7 @@ def resource_workstreams(topic_slug: str) -> str:
     match = next((t for t in topics if t["slug"] == topic_slug), None)
     if not match:
         return json.dumps({"error": f"Topic '{topic_slug}' not found"})
-    rows = _get("/workstreams", {"topic_id": match["id"]})
+    rows = _get("/workplans", {"topic_id": match["id"]})
     return json.dumps(
         {
             "_deprecation": _legacy_mcp_deprecation(resource="state://workstreams/{topic_slug}"),