fix: drop Marmot chatroom on leave so messages clear from caches

When the local user leaves a Marmot MLS group, MarmotManager already
wipes MLS state, the relay subscription and the persisted message log,
but the chatroom (and its decrypted inner messages) lingered in
marmotGroupList until the UI happened to call removeGroup. The CLI
leave path skipped that step entirely, and removeGroup itself only
dropped the chatroom from rooms — it left noteToGroupIndex entries and
the chatroom's own messages set in place, so notes stayed strongly
referenced and kept appearing in the Notification feed.

Move the in-memory cleanup into Account.leaveMarmotGroup, and have
MarmotGroupList.removeGroup also clear the chatroom's messages and the
note→group index. LocalCache holds notes weakly, so cutting the strong
refs is enough — GC reclaims them and the existing acceptableEvent
filter (which keys off marmotGroupList.rooms) hides anything still
in-flight.

amethyst/src/main/java/com/vitorpamplona/amethyst/model/Account.kt

@@ -2319,6 +2319,12 @@ class Account(
         }
 
         val outbound = manager.leaveGroup(nostrGroupId)
+        // manager.leaveGroup already wiped MLS state, relay subscriptions and
+        // the persisted message log. Drop the in-memory chatroom too — that
+        // releases the strong refs to the decrypted inner notes so LocalCache
+        // (which holds them weakly) can GC them, and the Notification feed
+        // (which iterates marmotGroupList.rooms) stops surfacing the group.
+        marmotGroupList.removeGroup(nostrGroupId)
         client.publish(outbound.signedEvent, groupRelays)
     }
 

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/marmotGroup/MarmotGroupInfoScreen.kt

@@ -316,7 +316,6 @@ fun MarmotGroupInfoScreen(
                 scope.launch(Dispatchers.IO) {
                     try {
                         accountViewModel.leaveMarmotGroup(nostrGroupId)
-                        accountViewModel.account.marmotGroupList.removeGroup(nostrGroupId)
                         nav.nav(Route.Message)
                     } catch (e: Exception) {
                         isLeaving = false