M7: release polish — export/import, docs, easy docker push

- Easy docker push (MQTTower ergonomics + the image push it lacks): VERSION file →
  version-tag.yml (semver-guard auto-tag) → docker-publish.yml (buildx multi-arch → GHCR,
  registry centralized for one-line retarget to git.finalfactory.de) + ci.yml + build-and-push.ps1.
- Verified end to end: deploy/Dockerfile builds; docker compose stack (app + timescaledb) comes
  up healthy; /healthz and the dashboard respond in-container.
- JSON config export/import (ExportService) with id remapping on restore + GET /export, POST
  /import endpoints; round-trip test preserves meter→type, meter-scoped tariff, category links.
- README, HA/Tasmota/MQTT wiring guide (docs/wiring.md), Unraid template.
- CLAUDE.md updated to reflect the built codebase.
- i18n: locale-aware number/currency formatting (de-DE); full de UI string localization deferred.

95 tests green (56 Core + 39 integration).

Claude-Session: https://claude.ai/code/session_01WujdMtMJPbxDpDnMeK22rr

deploy/build-and-push.ps1

@@ -0,0 +1,32 @@
+#!/usr/bin/env pwsh
+# Local convenience: build the multi-arch MeterVault image and push it.
+# Usage:  ./deploy/build-and-push.ps1 -Registry ghcr.io -Image finalfactory/metervault
+# Version is read from the VERSION file; images are tagged :<version> and :latest.
+
+param(
+    [string]$Registry = "ghcr.io",
+    [string]$Image = "finalfactory/metervault",
+    [string[]]$Platforms = @("linux/amd64", "linux/arm64"),
+    [switch]$Push
+)
+
+$ErrorActionPreference = "Stop"
+$root = Split-Path -Parent $PSScriptRoot
+$version = (Get-Content (Join-Path $root "VERSION")).Trim()
+$ref = "$Registry/$Image"
+
+Write-Host "Building $ref:$version ($($Platforms -join ', '))" -ForegroundColor Cyan
+
+$args = @(
+    "buildx", "build",
+    "--platform", ($Platforms -join ","),
+    "-f", (Join-Path $root "deploy/Dockerfile"),
+    "-t", "$ref`:$version",
+    "-t", "$ref`:latest"
+)
+if ($Push) { $args += "--push" } else { $args += "--load" }
+$args += $root
+
+& docker @args
+if ($LASTEXITCODE -ne 0) { throw "docker buildx build failed" }
+Write-Host "Done." -ForegroundColor Green