fix: readers see a remove button on a shared note's files (#33281)

Since a recent dev change, a reader opening a shared note sees the remove button on every file in the note, although clicking it does nothing. The editor was created editable and only switched to read-only afterwards, so the files were drawn as if the reader could edit. It now starts read-only for readers, and their files show without the button.

Fixes #33279

src/lib/components/common/RichTextInput.svelte

@@ -1051,6 +1051,7 @@
 				...(collaboration && provider ? [provider.getEditorExtension()] : [])
 			],
 			content: provider ? undefined : content,
+			editable,
 			autofocus: messageInput && !$showCallOverlay,
 			onTransaction: ({ transaction }) => {
 				if (!editor) return;