fix(cycle): keep the calendar feed to the owner and a managed profile's guardian

A calendar feed is a standing credential whose contents end up in a
third party's calendar cloud. Putting a record's cycle dates there is
the decision of the person they are about, or of the guardian of
somebody who cannot make it, and no delegate of an adult's record,
MANAGE included.

The subscription routes resolve through requireGuardianAuth instead of
requireRecordAuth("manage", "cycle"): the owner on their own record, or
a MANAGE grant on a record carrying the managed-profile marker. Every
verb follows, the revoke too. The feed re-reads the marker on each fetch
as well as the guardian's grant, so a row minted for somebody else on an
adult's record is a 404 whatever grant stands behind it. The settings
card is offered only where the routes answer.

The routes move from the delegable and MANAGE literals to the guardian
list, and the MANAGE handler inventory is back to 93.

docs/using/cycle-calendar-feed.md

@@ -13,9 +13,11 @@ dates on its servers, and turning the subscription off later does not remove
 copies it already holds. HealthLog asks you to confirm it is you (a password or
 passkey) and then shows the link once. Copy it, or use **Open in calendar app**.
 
-Only the record's owner, or someone who manages it with a MANAGE grant that
-covers cycle data, can turn it on. It is managed on the web; the iOS app shows
-where to find it.
+Only you can turn it on for your own record. For a managed profile (a child's
+record, for instance), its guardian can. Someone you have shared your record
+with cannot, whatever level of access you gave them: the feed puts your dates
+in their calendar provider's cloud, and that is your decision alone. It is
+managed on the web; the iOS app shows where to find it.
 
 ## Adding it to your calendar