feat(T-572): map SKIPPED in lib/job-status + alle terminal-checks

- lib/job-status.ts: SKIPPED ↔ 'skipped' mapping in beide richtingen
- components/shared/job-status.ts: label "Overgeslagen" + neutrale italic styling
- actions/admin/jobs.ts: cancel-guard erkent SKIPPED als eindstatus
- app/api/cron/cleanup-agent-artifacts: SKIPPED ook opruimen na 7d
- lib/insights/agent-throughput: SKIPPED telt mee als terminal

ACTIVE_JOB_STATUSES bewust ongewijzigd — SKIPPED is afgerond.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/api/cron/cleanup-agent-artifacts/route.ts

@@ -15,7 +15,7 @@ export async function POST(request: Request) {
 
   const { count: deleted } = await prisma.claudeJob.deleteMany({
     where: {
-      status: { in: ['FAILED', 'CANCELLED'] },
+      status: { in: ['FAILED', 'CANCELLED', 'SKIPPED'] },
       finished_at: { lt: cutoff },
     },
   })