Rename to Extended Media Forwards and forward rich message media

Rename the plugin (id extended_media_forwards) and add the Forward button
to media opened from rich messages, both single media and carousels.

Rich message media opens PhotoViewer through ChatActivity's
ChatArticlePageBlocksAdapter, whose parent object is the MessageObject
rather than a WebPage, so the article-only check hid the button. The
re-sent media links back to the message when it lives in a channel or
supergroup; elsewhere it is sent without a caption. FileLoader now gets
the parent object so expired file references can be refreshed.

Instant View carousels already worked: slideshow items are flattened
into the article's photo list. Findings are in docs/media-viewer-notes.md.

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

src/picker.py

@@ -89,4 +89,4 @@ def _enable_focus(alert):
         if alert.getWindow() is not None:
             alert.setFocusable(True)
     except Exception as exc:
-        log("[telegraph_media_forward] focus handoff failed: %s" % exc)
+        log("[extended_media_forwards] focus handoff failed: %s" % exc)