refactor: Extract hardcoded temperature query time ranges to constants

[Starosdev]

Summary

Extract hardcoded time range values in temperature/SMART attribute queries to named constants for better maintainability.

Why

Temperature history queries use hardcoded time range values instead of configurable constants, making it harder to adjust retention policies.

Files

• webapp/backend/pkg/database/scrutiny_repository_temperature.go (line 68)
• webapp/backend/pkg/database/scrutiny_repository_device_smart_attributes.go (line 40)

Acceptance Criteria

• Time range values extracted to named constants
• Constants defined in appropriate location (config or constants file)
• All usages updated to use constants
• No change in behavior