Server 2.6.2: log update checks and downloads; Go 1.27.3

The update relay logs every check (car, number of releases, newest
pre-release) and every download (car, file, size, then bytes and time,
or that it was cut short); never the forge's address or token, tested.
Go 1.27.3 for the build image and toolchain: govulncheck had found
GO-2026-6809 in crypto/x509 under 1.26.9; source and binary now clean.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LhzAVaUyqcw5PkGjz4mWW6

AGENTS.md

@@ -18,7 +18,7 @@ MG4 head unit (Android 9, AAOS, MT2712)
 - **app/** — Android app (Java, minSdk 27, runs on API 28). Reads the car through the
   `EVHardware/` library, shows it (Overview, Consumption, Charging), sends live data to the
   server and to ABRP, and updates itself.
-- **server/** — Go 1.26 API at `https://car.k8s.stinnesbeck.com`: stores telemetry, consumption
+- **server/** — Go 1.27 API at `https://car.k8s.stinnesbeck.com`: stores telemetry, consumption
   and charging in InfluxDB, pairs cars by QR code, carries settings typed on a phone, relays
   app releases from the private forge. It does **not** talk to ABRP. See `server/README.md`.
 - **k8s/** — plain Kubernetes manifests (InfluxDB, server, Grafana with three provisioned