Server: rewrite in Go as an API-only service

Same endpoints, request formats, validation rules and InfluxDB layout as
the Next.js server, so the car needs no change: POST /v1/telemetry,
PUT /v1/consumption/daily, PUT /v1/charging-sessions/{id}, GET
/v1/consumption/history/{id}, GET /v1/health. The dashboard, login and
the /v1/history reads are gone; Grafana takes over the dashboards.

- Go 1.26 standard library (net/http routing, log/slog) plus the
  official InfluxDB 2 client. Fails closed at startup on a missing
  InfluxDB setting or an ingest token under 24 characters.
- ABRP forwarder ported: newest fresh sample, rate limited, never
  queued, credentials only in the form body.
- 22 tests: validation, aggregation, forwarding, config, and the
  handlers through a fake store. govulncheck clean (x/net 0.60.0,
  toolchain go1.26.9).
- Image: static binary on distroless, about 11 MB, UID 65532, port
  8080; the build runs vet and the tests.
- Dev shell: Go, gopls and govulncheck instead of Node.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QLJfZQZeAKAwSqViTmLzki

flake.nix

@@ -112,7 +112,7 @@
         in
         {
           default = pkgs.mkShell {
-            packages = [ jdk android.androidsdk buildCar pkgs.nodejs_22 pkgs.influxdb2-server pkgs.influxdb2-cli ];
+            packages = [ jdk android.androidsdk buildCar pkgs.go pkgs.gopls pkgs.govulncheck pkgs.influxdb2-server pkgs.influxdb2-cli ];
 
             ANDROID_HOME = sdk;
             ANDROID_SDK_ROOT = sdk;