L7 Device Gateway v5.13.0 Hardening

[dcplatforms]

This submission implements the L7 Device Gateway's weekly mission for June 2026. Key updates include standardizing telemetry to 4-decimal strings for L11 ML parity, optimizing heartbeat indexing via Redis Hashes for large-scale fleet availability tracking, and normalizing individual DER alarms to ensure compatibility with L4 Market bidding penalties. Documentation and master status have been updated to reflect v5.13.0.

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PR created automatically by Jules for task 4985699999411288153 started by @dcplatforms

[google-labs-jules]

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