Tasks: Workspace details card

• T001 details.rs: derive the card and map PR status (unit test)
• T002 Card rows, Copy Path, Open Folder, PR link, Changes hand-off
• T003 Breadcrumb as a menu button; inactive without a workspace
• T004 Branch and pull-request symbolic icons, card CSS
• T005 GTK test; light/dark popover captures
• T006 Review fixes: undimmed inactive breadcrumb, latest task wins, card closes on workspace switch, readable PR and breadcrumb descriptions, details() unit tests