test(editor): cover read-only code-block branch; drop dead justify prop (#275 review F1/F2)

F1: add code-block-view.test.tsx (mirrors the footnote structure harness) asserting
the language selector renders only when editor.isEditable, and the copy button is
present in both modes.
F2: remove the now-dead justify=flex-end on the absolutely-positioned menu Group.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/client/src/features/editor/components/code-block/code-block-view.tsx

@@ -67,11 +67,7 @@ export default function CodeBlockView(props: NodeViewProps) {
         <NodeViewContent as="code" className={`language-${language}`} />
       </pre>
 
-      <Group
-        justify="flex-end"
-        contentEditable={false}
-        className={classes.menuGroup}
-      >
+      <Group contentEditable={false} className={classes.menuGroup}>
         {/* In read-only (published) there is no language selector at all —
             only the copy button. When editable the selector is hidden until
             the block is hovered/focused (or its dropdown is open) via the