fix(chat): the review's gaps — owner hand-over, live group lines, names, scroll, one tab's sound, uploads on disk, a chat button without the pet

- A group whose creator left or was deleted passes to its longest-standing
  member (ensureOwner), so it can still be managed.
- Group changes (added / removed / renamed / left) are sent live as
  chat_message and never count as unread, here or on the server.
- A disabled account is still named in old chats (people carries
  `disabled`) and never offered for a new one; a deleted one reads
  'Deleted user' instead of '?'.
- Load older keeps the message being read in place.
- With several tabs open only the first to see a message plays its sound /
  system notification (agenthub.chat.notified).
- The people list is read again on New chat and on every room change.
- Uploads go to <data dir>/chat/.incoming/ (multer disk storage) and are
  renamed into place — never held in memory; a refused one is removed.
- With the pet hidden, a chat button in the bottom-right corner (ChatDock,
  server mode) opens the same window, unread count and new-message card
  included.

server/openapi-extra/chat.js

@@ -83,7 +83,8 @@ const paths = {
     get: {
       tags: ["Chat"],
       summary: "Users the caller can chat with",
-      description: "Every enabled account but the caller: id, username, display name, avatar time.",
+      description:
+        "Every account but the caller: id, username, display name, avatar time, and `disabled` (not offered for a new chat).",
       responses: {
         200: {
           description: "People",
@@ -99,6 +100,10 @@ const paths = {
                     username: { type: "string" },
                     displayName: { type: "string", nullable: true },
                     avatarAt: { type: "string", nullable: true },
+                    disabled: {
+                      type: "boolean",
+                      description: "A disabled account: still named in old chats, never offered for a new one.",
+                    },
                   },
                 },
               },