feat: collect CPU temperature from DGX Sparks

[0xdfi]

Summary

DGX Spark nodes now report CPU temperature through the existing remote CPU metric instead of always returning 0. The collector reuses the host sensor allowlist and priority order, while filtering unrelated NVMe and network-card sensors.

Related: #34

Validation

• node --test server/collectors/__tests__/SystemCollector.cpuTemp.test.js - 8 passed, including the full remote DGX Spark parse path
• npm run typecheck - passed
• npm run build - passed
• Code review completed with no remaining actionable findings.

Post-Deploy Monitoring & Validation

• Search logs for Remote CPU error during the first 15 minutes.
• Compare the API CPU temperature with the first allowed hwmon or acpitz sensor on one DGX Spark.
• Healthy signal: a plausible non-zero Celsius value updates with each normal CPU poll.
• Failure signal: CPU polling fails, temperature exceeds the accepted sensor range, or the value comes from an NVMe/CX7 sensor. Roll back this PR if observed.
• Validation window and owner: first 15 minutes after deployment; sparkDash maintainer/operator.

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