Message Logger: hidden messages on the server, removed chats, old chat photos

- Hidden deleted messages are marked on the server (local marks migrated);
  "Reveal hidden messages" in the chat menu, Unhide in the message menu and
  the selection bar.
- Chats an account lost are reported, listed among its chats again and
  opened read-only with their logged messages, all deleted.
- Logged chat photos: a removed chat's avatar, and in a chat's photos the
  ones it no longer has, translucent with a trash icon in the viewer's
  previews.
- Fix: the deleted-post comments thread is answered locally again.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -22,9 +22,19 @@ the device, so a chat opened again, even offline, shows them at once.
   was closed are confirmed with Telegram and restored from the logger copy.
 - **Keep your own deletions.** The delete dialog gets a *Keep message for myself* checkbox: ticked,
   the deletion goes to Telegram but the message stays on this device, marked deleted.
-  Unticked (the default), it is deleted as usual and never restored from the logger here.
-  Deleting a message that is already deleted shows a plain dialog that removes it from view
-  on this device only.
+  Unticked (the default), it is deleted as usual and hidden, so it isn't restored from the
+  logger. Deleting a message that is already deleted shows a plain dialog that hides it.
+- **Hidden messages.** Hidden deleted messages are marked on the server, so every client
+  skips them. *Reveal hidden messages* in the chat's menu (Plugins) brings them back until
+  tapped again; a revealed one has *Unhide* in its menu, and selecting several shows an
+  Unhide button in the selection bar.
+- **Removed chats.** Chats an account lost (left, kicked, deleted by you or the other side)
+  stay in the chat list with their logged messages, read-only and all marked deleted, until
+  the chat is back. Chats you delete yourself aren't listed; deleting a listed one hides it.
+  *Show removed chats* in the settings turns this off.
+- **Old chat photos.** Chat photo changes are posted into the chat's log topic. A removed chat
+  shows its latest logged photo, and a chat's photos also list the logged ones it no longer
+  has: translucent, with a trash icon, in the photo viewer's previews.
 - **Edit history.** *Edit history* in the message menu (right above Forward, for edited
   messages) opens every version as a mock chat, also for the logger groups' own posts, with
   an *Open topic* button for the history topic in the activity group.
@@ -36,7 +46,7 @@ the device, so a chat opened again, even offline, shows them at once.
   going back returns to your account.
 - **Reset marks.** *Reset deleted/edited marks* in the chat's menu (Plugins) forgets that
   chat's cached marks and checks it with the server again; the same row in the plugin
-  settings does it for every chat. Messages you removed from view stay hidden.
+  settings does it for every chat. Hidden messages stay hidden.
 - **Cache lifetime.** Cached answers are kept for 1, 7, 30, 90 or 365 days, or forever
   (30 by default).