feat(subgroups): put the ceremony that needs you at the bottom of the chat

A NIP-17 room already showed the standing "waiting for your signature" notice
under the newest message -- `ProposalsAwaitingYouNotice` is transport-agnostic and
reads `FrostSigningSession` by room. What it never covered is the other thing a
room can owe somebody, which in a NIP-17 room is the main thing: a ceremony.

That gap matters more here than the signing one does. A ChillDKG cannot finish
until **every** member has taken part, so one member not finding their request
stalls everyone indefinitely -- and the only way to find it was to scroll the
transcript to its request line, past whatever else the room has been used for.
Three subgroups on the connected devices sat at 1 of 3 host keys for exactly that
reason.

`CeremoniesAwaitingYouNotice` sits beside the signing one, first in the reversed
layout so a room owing both puts the ceremony nearest the composer -- until a
ceremony finishes there is no key to sign anything with.

**It covers two different kinds of owing, and the second has no gate behind it.**
A participant is owed an approval, read through the same `pendingApproval` the
ritual screen uses so the two cannot disagree. The member who *opened* it is owed
something the protocol has no gate for: a ceremony reaching COMPLETE finishes
nothing on its own -- the group has a key and somebody still has to get its state
signed and create the room -- and that somebody is whoever opened it. Nothing else
in the app would ever say so, which is what the coordinator was missing.

`roomAwaitingCreation` is how it knows when to stop: the room a finished ceremony's
key derives either exists or does not. Asking that rather than keeping a flag means
the notice cannot become permanent furniture in every room that has ever held a
ceremony.

**It reads every ceremony in the room, not the newest.** A room holds more than one
the moment a subgroup's admins are the whole group, and the one that wants you is
routinely not the one that happened last -- that is what buried 2.0 and 2.1. The
notice opens the ceremony it names, by session id, through the same
`onOpenSharedKey` the transcript's own lines use since `0b65d702`.

Unlike the signing notice it opens the ceremony rather than a queue: there is no
queue of ceremonies, and with several the count is shown and the newest opened.

Eight strings in the catalogue in sentence case, each step worded the way its
approval screen words it so a member is not asked twice in two vocabularies.
`dkgRepository` is threaded to `ChatMessageListViewModel` through the messaging
screen, the home pane and the nav host.

397 common tests, 718 jvm tests, `m3Audit` meets every budget with 0 title-case
strings and 0 dp literals.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

composeApp/src/commonMain/composeResources/values/strings.xml

@@ -390,4 +390,12 @@
     <string name="before_the_subgroup_exists_its_parent_signs">Before the subgroup exists, its parent signs for it. That signature is what lets anyone check where this group came from.</string>
     <string name="ask_the_parent_group_to_certify">Ask the parent group to certify this subgroup</string>
     <string name="create_the_subgroup">Create the subgroup</string>
+    <string name="the_key_ceremony_needs_you">The key ceremony needs you</string>
+    <string name="the_subgroups_key_ceremony_needs_you">The subgroup's key ceremony needs you</string>
+    <string name="ceremonies_need_you">%1$s key ceremonies need you</string>
+    <string name="join_the_ceremony_by_publishing_your_key">Join it by publishing your device's key</string>
+    <string name="send_your_contribution_to_the_key">Send your contribution to the key</string>
+    <string name="check_the_combined_result">Check the combined result and confirm it</string>
+    <string name="the_group_has_its_key_finish_setting_it_up">The group has its key — finish setting it up</string>
+    <string name="open">Open</string>
 </resources>