chore(log): align levels with the documented convention

Three places disagreed with AGENTS' own level rules: get_chat/get_chat_administrators failures during /set_channel printed at error even though the usual cause is a mistyped channel name the user fixes on the spot (error is reserved for dead letters and the like — now warn, same as other user-served degradations); the edit-before-forward callback arrival line logged at info while the sibling arrival lines for commands and inline queries log at debug (now debug, still carries the escaped payload); and the two upload-fallback lines logged at info while photo.rs's parallel degradations log at warn (now warn both — Telegram failing to fetch our media is a degradation that leaves the user served). AGENTS' convention sentence is now explicit about all three instead of the ambiguous '(fallback, retry enqueue, dead-letter is error)'.

crates/xmedia-bot/src/handlers/callback.rs

@@ -71,7 +71,7 @@ async fn handle_callback(
         return;
     }
 
-    log::info!(
+    log::debug!(
         "callback from {chat_id} on prompt {prompt_message_id}: {}",
         super::log_escape(data)
     );