Project detail: group issues by status like the Issues list

The project detail page showed a flat issue list; the main Issues list groups issues into collapsible workflow-status sections. Carry that grouping over for consistency.

Extracted the Issues-list grouping into a shared IssueGroups component (collapsible status sections ordered by the viewer's category order then board position, with caret + status dot + count) and used it on the project detail page (showProject={false}). Identical look on desktop + mobile.