feat(audio-rooms): in-feed Join button closes deep-link loop

A `nostr:naddr1...` for a kind-30312 routes through MainActivity's
URI handler to Route.Note(addressTag) and lands on the
RenderMeetingSpaceEvent renderer in the note view. Until now that
renderer only showed the room name + summary + participant list —
there was no way to actually enter the room without going through
the live-activity ChannelView lobby (which is for kind-30311).

Extract the Join button from AudioRoomJoinCard into a standalone
JoinAudioRoomButton composable, then drop it into the note-view
renderer. Hidden when status=CLOSED (you can't join a finished
room) or when the event lacks service/endpoint/d-tag. Single
helper means the lobby card and the in-feed button share the
same launch logic; future surfaces (room list, search results)
can add the same button trivially.

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/note/types/MeetingSpace.kt

@@ -22,6 +22,7 @@ package com.vitorpamplona.amethyst.ui.note.types
 
 import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
@@ -158,6 +159,24 @@ fun RenderMeetingSpaceEventInner(
     }
 
     RenderParticipants(participants, accountViewModel, nav)
+
+    // In-feed Join button — closes the deep-link loop. A
+    // `nostr:naddr1...` for a kind-30312 lands here through
+    // MainActivity's URI handler → Route.Note(addressTag) → this
+    // renderer; without a button the user has no path into the
+    // audio room. JoinAudioRoomButton hides itself when the
+    // event lacks service / endpoint / d-tag.
+    if (status != MeetingSpaceStatusTag.STATUS.CLOSED) {
+        Row(
+            modifier = Modifier.fillMaxWidth().padding(top = 8.dp),
+            horizontalArrangement = Arrangement.End,
+        ) {
+            com.vitorpamplona.amethyst.ui.screen.loggedIn.audiorooms.room.JoinAudioRoomButton(
+                event = noteEvent,
+                accountViewModel = accountViewModel,
+            )
+        }
+    }
 }
 
 @Composable

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/audiorooms/room/AudioRoomJoinCard.kt

@@ -107,21 +107,48 @@ private fun AudioRoomJoinCardContent(
                 horizontalArrangement = Arrangement.End,
                 verticalAlignment = Alignment.CenterVertically,
             ) {
-                Button(onClick = {
-                    AudioRoomBridge.set(accountViewModel)
-                    AudioRoomActivity.launch(
-                        context = context,
-                        addressValue = addressValue,
-                        authBaseUrl = serviceBase,
-                        endpoint = endpoint,
-                        hostPubkey = hostPubkey,
-                        roomId = roomId,
-                        kind = kind,
-                    )
-                }) {
-                    Text(stringRes(R.string.audio_room_join))
-                }
+                JoinAudioRoomButton(event = event, accountViewModel = accountViewModel)
             }
         }
     }
 }
+
+/**
+ * Standalone "Join audio room" button. Reusable from any composable
+ * that has a [MeetingSpaceEvent] in hand — the lobby card, the
+ * in-feed note renderer (so a `nostr:naddr1...` deep-link to a
+ * kind-30312 lands one tap away from the room), and any future
+ * room-list surface. Renders nothing for events without a
+ * service / endpoint / d-tag — those rooms can't be joined on
+ * the audio plane.
+ */
+@Composable
+fun JoinAudioRoomButton(
+    event: MeetingSpaceEvent,
+    accountViewModel: AccountViewModel,
+) {
+    val serviceBase = event.service()
+    val endpoint = event.endpoint()
+    val roomId = event.address().dTag
+    if (serviceBase.isNullOrBlank() || endpoint.isNullOrBlank() || roomId.isBlank()) return
+
+    val context = LocalContext.current
+    val addressValue = remember(event) { event.address().toValue() }
+    val hostPubkey = event.pubKey
+    val kind = event.kind
+
+    Button(onClick = {
+        AudioRoomBridge.set(accountViewModel)
+        AudioRoomActivity.launch(
+            context = context,
+            addressValue = addressValue,
+            authBaseUrl = serviceBase,
+            endpoint = endpoint,
+            hostPubkey = hostPubkey,
+            roomId = roomId,
+            kind = kind,
+        )
+    }) {
+        Text(stringRes(R.string.audio_room_join))
+    }
+}