Mark units as golden or failing samples

Reference units can now be tagged as known-good (golden) or known-faulty (failing) so they're excluded from production analytics and FPY/Cpk stay honest.

• Added a sample classification dropdown on the unit detail page with activity tracking
• Added a sidebar filter and table avatar treatment for golden and failing samples
• Surfaced the sample field in V2 API for unit and run get/list/create/update