feat(api,userbot,frontend): search peers without chats and start tracking them

frontend/src/lib/components/ChatHeader.svelte

@@ -15,6 +15,7 @@
   import { formatPresence } from "$lib/format/presence";
   import { accounts } from "$lib/stores/accounts.svelte";
   import { chats } from "$lib/stores/chats.svelte";
+  import { discover } from "$lib/stores/discover.svelte";
   import { events } from "$lib/stores/events.svelte";
   import { toasts } from "$lib/stores/toasts.svelte";
   import { ui } from "$lib/stores/ui.svelte";
@@ -27,6 +28,7 @@
 
   const isDm = $derived(chatId > 0);
   const chat = $derived(chats.byId(chatId));
+  const discovered = $derived(discover.get(chatId));
   let peer = $state<PeerView | null>(null);
   let presence = $state<PresenceSample | null>(null);
   let backfilling = $state(false);
@@ -46,6 +48,13 @@
     }
   }
 
+  $effect(() => {
+    if (accounts.selectedId === null) {
+      return;
+    }
+    discover.ensure(chatId).catch(() => undefined);
+  });
+
   $effect(() => {
     if (accounts.selectedId === null || !isDm) {
       peer = null;
@@ -103,7 +112,9 @@
   });
 
   const fallbackTitle = $derived(
-    chat?.title ?? (isDm ? "Удалённый аккаунт" : `Chat ${chatId}`)
+    chat?.title ??
+      discovered?.title ??
+      (isDm ? "Удалённый аккаунт" : `Chat ${chatId}`)
   );
   const title = $derived(isDm && peer ? peerName(peer) : fallbackTitle);
   const subtitle = $derived.by(() => {
@@ -116,11 +127,16 @@
       }
       return peer?.phone ?? `ID ${chatId}`;
     }
-    const count = chat?.message_count ?? 0;
-    return count > 0 ? `${count} messages` : "group";
+    const count = chat?.message_count ?? discovered?.message_count ?? 0;
+    if (count > 0) {
+      return `${count} messages`;
+    }
+    return discovered?.kind === "channel" ? "channel" : "group";
   });
   const avatarKind = $derived(isDm ? "peer" : "chat");
-  const hasAvatar = $derived(chat?.has_avatar ?? Boolean(peer?.has_avatar));
+  const hasAvatar = $derived(
+    chat?.has_avatar ?? Boolean(peer?.has_avatar || discovered?.has_avatar)
+  );
 </script>
 
 <header class="chat-header">