ci: make the deferred planning benchmark non-blocking

Run the unchanged benchmark as a separate advisory job while #78 is open.
Keep functional coverage and other checks required, and retain the 2 GB heap
and 300-second protocol limit. Record #78's obligation to restore the gate.

Refs: #75, #78

docs/planning-objectives.md

@@ -279,5 +279,8 @@ Ticket #75 covers saved-rule migration and functional integration of #70–#75.
 Performance acceptance and any further optimization are tracked in #78, after
 original-decision-trace removal in #76 and functional verification in #77. The
 seven-scenario benchmark, its warm-up and two measured repetitions, the 2 GB heap
-limit and the 300-second timeout remain unchanged. Completing the functional
-migration does not establish that these performance gates pass.
+limit and the 300-second timeout remain unchanged. CI runs the benchmark as a
+separate non-blocking job at the user's request while #78 is open; functional
+tests and other checks remain required. #78 must restore the required benchmark
+gate after the protocol passes. Completing the functional migration or passing
+CI during this exception does not establish a passing benchmark.