perf(test-e2e-playwright): order Playwright passes by meta/tests.yml run_after

A role's playwright.run_after names the roles its pass runs after; the new
playwright_order lookup reads it through role_tests (which now renders
Jinja with the queried role as application_id) and orders the round with
a stable topological sort, so only constrained roles move. web-app-docs
runs after every other invokable role: in CI run 41206003651 (Discourse#2)
its pass waited 3126 s for the docs server's Sphinx build while stalwart,
bigbluebutton, jitsi and prometheus (~400 s) queued behind it. Cycles,
self references, unknown roles and non-list values fail loudly.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/python/utils/roles/test_order.py

@@ -13,6 +13,7 @@ from utils.roles.order import (
     build_dependency_graph,
     find_cycle,
     ordered_roles,
+    stable_order_after,
     topological_sort,
 )
 
@@ -82,5 +83,37 @@ class TestRoleOrder(unittest.TestCase):
             ordered_roles(self.temp_dir, "grp")
 
 
+class TestStableOrderAfter(unittest.TestCase):
+    NAMES = ("keycloak", "matomo", "docs", "stalwart", "jitsi")
+
+    def test_no_constraint_keeps_the_order(self):
+        self.assertEqual(stable_order_after(list(self.NAMES), {}), list(self.NAMES))
+
+    def test_a_name_after_all_others_moves_last_and_nothing_else_moves(self):
+        others = [name for name in self.NAMES if name != "docs"]
+        result = stable_order_after(list(self.NAMES), {"docs": others})
+        self.assertEqual(result, [*others, "docs"])
+
+    def test_a_satisfied_constraint_moves_nothing(self):
+        result = stable_order_after(list(self.NAMES), {"stalwart": ["matomo"]})
+        self.assertEqual(result, list(self.NAMES))
+
+    def test_names_outside_the_list_constrain_nothing(self):
+        result = stable_order_after(
+            list(self.NAMES), {"matomo": ["absent"], "docs": ["jitsi", "gone"]}
+        )
+        self.assertEqual(result, ["keycloak", "matomo", "stalwart", "jitsi", "docs"])
+
+    def test_a_name_listing_itself_raises(self):
+        with self.assertRaises(RuntimeError):
+            stable_order_after(list(self.NAMES), {"docs": ["docs"]})
+
+    def test_a_cycle_raises_and_names_its_members(self):
+        with self.assertRaises(RuntimeError) as ctx:
+            stable_order_after(list(self.NAMES), {"docs": ["jitsi"], "jitsi": ["docs"]})
+        self.assertIn("docs", str(ctx.exception))
+        self.assertIn("jitsi", str(ctx.exception))
+
+
 if __name__ == "__main__":
     unittest.main()