matrix-synapse: route the current Nheko summary endpoint

Synapse currently supports both the deprecated
`/_matrix/client/unstable/im.nheko.summary/rooms/<room>/summary`
route and the recommended
`/_matrix/client/unstable/im.nheko.summary/summary/<room>`
form. MDAD only matched the deprecated shape.

Add the recommended pattern alongside the old one so worker routing
matches the current upstream API surface while preserving backward
compatibility for the deprecated path.

Refs:
- b99a58719b/docs/workers.md (synapseappgeneric_worker)
- b99a58719b/synapse/rest/client/room.py (L1716-L1728)

roles/custom/matrix-synapse/vars/main.yml

@@ -200,6 +200,7 @@ matrix_synapse_workers_generic_worker_endpoints:
   - ^/_matrix/client/(v1|unstable)/rooms/.*/relations/
   - ^/_matrix/client/v1/rooms/.*/threads$
   - ^/_matrix/client/unstable/im.nheko.summary/rooms/.*/summary$
+  - ^/_matrix/client/unstable/im.nheko.summary/summary/.*$
   - ^/_matrix/client/(r0|v3|unstable)/account/3pid$
   - ^/_matrix/client/(r0|v3|unstable)/account/whoami$
   - ^/_matrix/client/versions$