Add component for grouped thumbnails

Editor assessment

'Add component for grouped thumbnails' hits the basics well: feat is right for a new component, 'Add' is imperative, and the header is short and specific. Two gaps: no scope (gallery or conversation would help grouping), and no body explaining what 'grouped' means — grouping by sender? by date? collapsing stacks of images? — which is exactly the kind of design intent a component commit should record. The PR number preserves the discussion for those willing to click through. A fine changelog line and a thin historical record; one extra sentence would have balanced both.