Collapse sections by clicking title bar instead of a dedicated button

Instead of having collapse buttons on the main view components/categories, clicking the title bars should collapse them.

Acceptance criteria

Clicking a section's title bar toggles its collapsed/expanded state.
Dedicated collapse buttons are removed (or repurposed as a visual indicator only, e.g. a chevron, without being the sole click target).
Title bar remains usable for any other existing interactions (if any) without conflicting with the collapse click.