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

server/days.go

@@ -0,0 +1,51 @@
+package main
+
+import "sort"
+
+// aggregateDays folds chunks into days, newest day first, each with its running lifetime
+// total. Pure, so the arithmetic is tested without a database.
+func aggregateDays(chunks []ConsumptionChunk) []DailyConsumption {
+	type day struct {
+		DailyConsumption
+		sohAt  int64
+		hasSoh bool
+	}
+	byDate := map[string]*day{}
+	for _, chunk := range chunks {
+		d, ok := byDate[chunk.Date]
+		if !ok {
+			d = &day{DailyConsumption: DailyConsumption{
+				InstallationID: chunk.InstallationID,
+				Date:           chunk.Date,
+				RecordedAt:     chunk.RecordedAt,
+			}}
+			byDate[chunk.Date] = d
+		}
+		d.Day.add(chunk.Day)
+		if chunk.RecordedAt.After(d.RecordedAt) {
+			d.RecordedAt = chunk.RecordedAt
+		}
+		// The newest manual SoH of the day wins.
+		at := chunk.RecordedAt.UnixMilli()
+		if chunk.SohPercent != nil && (!d.hasSoh || at > d.sohAt) {
+			soh := *chunk.SohPercent
+			d.SohPercent = &soh
+			d.sohAt = at
+			d.hasSoh = true
+		}
+	}
+	days := make([]DailyConsumption, 0, len(byDate))
+	for _, d := range byDate {
+		days = append(days, d.DailyConsumption)
+	}
+	sort.Slice(days, func(i, j int) bool { return days[i].Date < days[j].Date })
+	var running Totals
+	for i := range days {
+		running.add(days[i].Day)
+		days[i].Lifetime = running
+	}
+	for i, j := 0, len(days)-1; i < j; i, j = i+1, j-1 {
+		days[i], days[j] = days[j], days[i]
+	}
+	return days
+}