feat(server): admin users list surfaces is_test_account

UserDetails carries the new column, search_users selects and
optionally filters on it, and the /api/admin/users route accepts
?include_test=false to hide soak-harness accounts.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/routers/admin.py

@@ -84,6 +84,7 @@ async def list_users(
     offset: int = 0,
     include_banned: bool = True,
     include_deleted: bool = False,
+    include_test: bool = True,
     admin: User = Depends(require_admin_v2),
     service: AdminService = Depends(get_admin_service_dep),
 ):
@@ -96,6 +97,10 @@ async def list_users(
         offset: Results to skip.
         include_banned: Include banned users.
         include_deleted: Include soft-deleted users.
+        include_test: Include soak-harness test accounts (default true).
+            Admins see all accounts by default; pass ?include_test=false
+            to hide test accounts. Public stats endpoints default to
+            hiding them.
     """
     users = await service.search_users(
         query=query,
@@ -103,6 +108,7 @@ async def list_users(
         offset=offset,
         include_banned=include_banned,
         include_deleted=include_deleted,
+        include_test=include_test,
     )
     return {"users": [u.to_dict() for u in users]}