refactor(send): media_from reads the thumbnail off the item itself

All three callers passed item.thumbnail_url() as the fourth argument — a parameter that could never vary without defeating its own purpose, and only the video arm ever reads it. The function takes the item already; it asks the item. Three call sites lose an argument.

crates/xmedia-bot/src/send/upload.rs

@@ -189,7 +189,7 @@ fn media_from_file(
     path: std::path::PathBuf,
     caption: Option<&str>,
 ) -> Result<InputMedia, String> {
-    media_from(item, InputFile::file(path), caption, item.thumbnail_url())
+    media_from(item, InputFile::file(path), caption)
 }
 
 /// Builds the media group item from a (smaller) URL.
@@ -198,7 +198,7 @@ fn media_from_url(
     url: &str,
     caption: Option<&str>,
 ) -> Result<InputMedia, String> {
-    media_from(item, input_file_for(url)?, caption, item.thumbnail_url())
+    media_from(item, input_file_for(url)?, caption)
 }
 
 /// One item prepared for the upload fallback: the ready-to-send media plus