feat(884): persistent perm_rx lock-holder for Matrix bot

Before: handle_message.rs acquired services.perm_rx only while processing
one chat message and dropped it on chat_fut completion. The moment the
bot wasn't actively responding, prompt_permission auto-denied any spawned
coder bash call as "no interactive session" — making unattended coder
work impossible.

Now: a permission_listener task is spawned at bot startup and holds
perm_rx for the bot's lifetime. Permission requests are forwarded to
the first configured Matrix room, replies resolved by the existing
on_room_message handler via pending_perm_replies. Per-message acquire is
gone from handle_message.rs (chat_fut just awaits cleanly).

- New module: chat/transport/matrix/bot/permission_listener.rs.
- Wired into run_bot before BotContext construction; bot_sent_event_ids
  is hoisted out so the listener and the rest of the bot share it.
- handle_message.rs no longer touches perm_rx.
- diagnostics/permission.rs comment updated to reflect the new reality.
- Regression test asserts the listener forwards a PermissionForward to
  the target room and records the pending reply key — exactly the path
  that was broken when no chat_fut was in flight.

Discord/Slack/WhatsApp transports still acquire perm_rx per message
(commands.rs:368 / commands/llm.rs:83 / commands/llm.rs:82). They are
not the active transport in this deployment so their per-message acquire
remains dormant; the same listener pattern should be applied to them as
follow-up work in 884 phase 2.

server/src/chat/transport/matrix/bot/run.rs

@@ -275,6 +275,26 @@ pub async fn run_bot(
         }
     }
 
+    // Hoist bot_sent_event_ids out of BotContext so the permission listener
+    // can share it (the listener tracks which permission-prompt messages it
+    // posted so the bot doesn't echo them back as user input).
+    let bot_sent_event_ids: Arc<TokioMutex<HashSet<matrix_sdk::ruma::OwnedEventId>>> =
+        Arc::new(TokioMutex::new(HashSet::new()));
+
+    // Spawn the permission listener: holds `perm_rx` for the bot's lifetime
+    // and forwards permission requests to the first configured room. Story
+    // 884 — replaces the per-message lock acquire previously done in
+    // handle_message.rs, so spawned coders' bash calls reach chat even when
+    // the bot isn't actively responding.
+    if let Some(target_room) = target_room_ids.first() {
+        super::permission_listener::spawn_permission_listener(
+            Arc::clone(&services),
+            Arc::clone(&transport),
+            target_room.clone(),
+            Arc::clone(&bot_sent_event_ids),
+        );
+    }
+
     let ctx = BotContext {
         services,
         matrix_user_id: bot_user_id,
@@ -282,7 +302,7 @@ pub async fn run_bot(
         allowed_users: config.allowed_users,
         history: Arc::new(TokioMutex::new(persisted)),
         history_size: config.history_size,
-        bot_sent_event_ids: Arc::new(TokioMutex::new(HashSet::new())),
+        bot_sent_event_ids,
         htop_sessions: Arc::new(TokioMutex::new(HashMap::new())),
         transport: Arc::clone(&transport),
         timer_store,