Add assignment-layer runtime smoke checklist #60

Before agents relies on Mission Control for assignment, the app needs a clear runtime smoke checklist.

Document checks for:

• GET /api/health returns healthy.
• POST /api/automation/sync succeeds.
• GET /api/automation/repos returns repos.
• POST /api/sync returns syncedCount > 0.
• GET /api/issues returns issues.
• Board shows issues.
• Projects shows repo groups.
• Agent heartbeat/run events appear in Agents.
• Queue endpoint returns candidate issues.
• Claiming a low-risk test issue updates GitHub labels.
• Claiming writes an AuditLog entry.
• Unclaiming or reverting the test issue works.
• Logs show no Prisma, BigInt, or FK errors.
• Mission Control failures do not break agent runs.