chore: move stray NIP-29 section comment to AccountRelayGroupActions

The relay-group section header and joinRelayGroup KDoc were left
dangling at the end of AccountConcordActions when the clusters were
split into separate files; reattach them to the function they describe.
Found by the post-refactor audit.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012sJgKJ4FAjcZqvkMc7U3EA

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

@@ -1055,11 +1055,4 @@ class AccountConcordActions(
         account.client.fetchAllPagesFromPool(filters = byRelay) { _, _ -> drained++ }
         Log.d("Concord", "syncConcordControlPlanes: paged ${authorsByRelay.size} relay(s), drained $drained control wrap(s)")
     }
-
-    // ── NIP-29 relay-group actions ───────────────────────────────────────────
-    // All group commands are published ONLY to the group's host relay, where
-    // relay29 authorizes them. The relay is the source of truth; the kind-10009
-    // list is our own cross-device bookkeeping of what we joined.
-
-    /** Send a kind 9021 join request to the group's host relay and remember it. */
 }

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

@@ -82,6 +82,11 @@ import kotlinx.serialization.json.Json
 class AccountRelayGroupActions(
     private val account: Account,
 ) {
+    // All group commands are published ONLY to the group's host relay, where
+    // relay29 authorizes them. The relay is the source of truth; the kind-10009
+    // list is our own cross-device bookkeeping of what we joined.
+
+    /** Send a kind 9021 join request to the group's host relay and remember it. */
     suspend fun joinRelayGroup(
         channel: RelayGroupChannel,
         code: String? = null,