health: fix tautological healthy flag in scheduler health check

[ng]

Problem

CodeRabbit identified that the healthy flag in the scheduler health endpoint may be tautological (always evaluating to true).

File: src/server/routers/health.ts:81-86

Current logic:

const healthy = jobs.length > 0 || jobCounts.total === 0

CodeRabbit's concern: Since jobCounts.total === jobs.length, this expression is always true.

Analysis Needed

Need to verify:

1. Is this actually a tautology?
2. What should "healthy" actually mean for the scheduler?
   • Should it check scheduler.isEnabled() && jobs.length > 0?
   • Should it compare against expected job count from DB?
   • Should it verify no jobs are in error state?

Proposed Solution

Replace with meaningful health check:

const healthy = scheduler.isEnabled() 
  ? jobs.length > 0  // If enabled, should have at least one job
  : jobCounts.total === 0  // If disabled, should have no jobs

Or compare against expected job count:

const [settings] = await db.select().from(deviceSettings).limit(1)
const expectedJobs = computeExpectedJobCount(settings)
const healthy = jobCounts.total === expectedJobs

Priority

Medium - Health checks are important for monitoring and alerting

References

• PR feat(scheduler): add job scheduling system with production-ready reliability fixes #111 - Job Scheduler Implementation
• CodeRabbit Review Comment (src/server/routers/health.ts:81-86)
• Commit: 801872f (CodeRabbit review fixes)