debug(marmot): log removeMarmotGroupMember + syncMetadataTo transitions

The bug report: after tapping Remove on the Marmot Group Info screen,
the target npub stays in the member list, and the only log line is
the round-tripped kind:445 hitting the "Duplicate" branch in
GroupEventHandler.add. The author-side path (Account.removeMarmotGroupMember
→ MarmotManager.removeMember → syncMetadataTo → publish) has no logging,
so there's no way to tell which step broke — the MLS tree mutation,
the local member-list push to chatroom.members, or the UI recomposition.

Mirror the addMarmotGroupMember logging style on removeMarmotGroupMember
(entry, no-op guards, built commit id, publish) so we can see whether
the author path even runs end-to-end, and have syncMetadataTo log the
group id and the previous→new member count so the StateFlow update
becomes observable. No behavior change.

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/marmot/MarmotManager.kt

@@ -566,9 +566,14 @@ class MarmotManager(
             chatroom.adminPubkeys.value = metadata.adminPubkeys
             chatroom.relays.value = metadata.relays
         }
+        val previousCount = chatroom.members.value.size
         val members = memberPubkeys(nostrGroupId)
         chatroom.members.value = members
         chatroom.memberCount.value = members.size
+        Log.d("MarmotDbg") {
+            "syncMetadataTo: group=${nostrGroupId.take(8)}… members $previousCount→${members.size} " +
+                "(leafs=${members.map { it.leafIndex }})"
+        }
     }
 }