[3] [TASK] [Backend] [Validation] Implement TelemetryValidator for semantic validation

[R4R35]

Description

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Create a TelemetryValidator component that performs semantic validation on incoming pings after structural validation passes. This drops pings that are structurally valid but logically impossible (e.g. coordinates in the ocean, future timestamps).

Scope

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• Create TelemetryValidator as a @Component
• Validate lat is between -90 and 90
• Validate lng is between -180 and 180
• Validate accuracyMeters is positive
• Validate timestamp is not in the future
• Integrate validator in TelemetryService before saving

Done When

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• Pings with invalid coordinates are rejected and logged
• Pings with future timestamps are rejected and logged
• Valid pings are still saved correctly to MongoDB

Priority

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• 🔴 High