feat(deploy): Traefik active-leader routing + docker-dev compose (Task 63)

- scripts/install/traefik.yml + traefik-dynamic.yml: Traefik static + dynamic
  config. One :80 entry point, one router on HostRegexp(otopcua.*), one
  service load-balancing admin-a:9000 + admin-b:9000 with /health/active health
  check (interval 5s, timeout 2s, expected 200). Followers return 503 from
  /health/active so Traefik drops them within the next interval after a
  leadership change.

- scripts/install/Install-Traefik.ps1: downloads Traefik for Windows, drops the
  yml configs, registers the OtOpcUaTraefik Windows service via sc.exe with
  restart-on-failure. Companion to Install-Services.ps1.

- docker-dev/{Dockerfile,docker-compose.yml,traefik-dynamic.yml,README.md}:
  Mac-friendly four-node fleet (admin-a + admin-b + driver-a + driver-b) plus
  SQL Server 2022 + OpenLDAP + Traefik. Single OtOpcUa.Host image built once;
  Compose drives OTOPCUA_ROLES + Cluster:* per container to differentiate the
  four hosts. README walks through bring-up + failover smoke + the dev LDAP
  users.

Note: untested on macOS (no local Docker — see docs/v2/dev-environment.md).

scripts/install/Install-Traefik.ps1

@@ -0,0 +1,68 @@
+<#
+.SYNOPSIS
+    Installs Traefik as a Windows service that routes admin HTTP traffic to whichever
+    OtOpcUa.Host node holds the admin role-leader (via /health/active).
+
+.DESCRIPTION
+    Downloads the Traefik Windows binary into $InstallRoot, drops traefik.yml +
+    traefik-dynamic.yml from this directory next to it, and registers Traefik as a
+    Windows service via sc.exe with restart-on-failure.
+
+    Companion to Install-Services.ps1. Run on the box that fronts the admin HTTP
+    traffic (typically a separate node from OtOpcUaHost, or co-located on the
+    primary admin node).
+
+.PARAMETER InstallRoot
+    Where the Traefik binary + config land. Default 'C:\Program Files\Traefik'.
+
+.PARAMETER TraefikVersion
+    Traefik version to download. Default 'v3.1.6'.
+
+.EXAMPLE
+    .\Install-Traefik.ps1 -InstallRoot 'C:\Program Files\Traefik'
+#>
+[CmdletBinding()]
+param(
+    [string]$InstallRoot = 'C:\Program Files\Traefik',
+    [string]$TraefikVersion = 'v3.1.6'
+)
+
+$ErrorActionPreference = 'Stop'
+
+if (-not (Test-Path $InstallRoot)) {
+    New-Item -ItemType Directory -Path $InstallRoot | Out-Null
+}
+
+$zip = Join-Path $env:TEMP "traefik-$TraefikVersion.zip"
+$url = "https://github.com/traefik/traefik/releases/download/$TraefikVersion/traefik_${TraefikVersion}_windows_amd64.zip"
+
+Write-Host "Downloading Traefik $TraefikVersion..."
+Invoke-WebRequest -Uri $url -OutFile $zip
+Expand-Archive -Path $zip -DestinationPath $InstallRoot -Force
+Remove-Item $zip
+
+$scriptDir = Split-Path -Parent $MyInvocation.MyCommand.Path
+Copy-Item -Force (Join-Path $scriptDir 'traefik.yml') $InstallRoot
+Copy-Item -Force (Join-Path $scriptDir 'traefik-dynamic.yml') (Join-Path $InstallRoot 'dynamic.yml')
+
+# Traefik reads dynamic.yml from /etc/traefik on Linux; on Windows place it next to the
+# binary and point the file provider at it. Edit traefik.yml's `filename:` if you want
+# to change the location.
+(Get-Content -Raw (Join-Path $InstallRoot 'traefik.yml')) `
+    -replace '/etc/traefik/dynamic.yml', (Join-Path $InstallRoot 'dynamic.yml').Replace('\', '/') `
+    | Set-Content (Join-Path $InstallRoot 'traefik.yml')
+
+Write-Host "Installing Traefik Windows service..."
+& sc.exe create OtOpcUaTraefik binPath= "`"$InstallRoot\traefik.exe`" --configFile=`"$InstallRoot\traefik.yml`"" `
+    DisplayName= 'OtOpcUa Traefik (admin HTTP front door)' `
+    start= auto | Out-Null
+
+& sc.exe failure OtOpcUaTraefik reset= 86400 actions= restart/5000/restart/30000/restart/60000 | Out-Null
+
+Write-Host ""
+Write-Host "Installed OtOpcUaTraefik. Edit:"
+Write-Host "  $InstallRoot\dynamic.yml  (router + service definitions)"
+Write-Host "Start with:"
+Write-Host "  sc.exe start OtOpcUaTraefik"
+Write-Host ""
+Write-Host "Traefik dashboard: http://localhost:8080  (turn off api.insecure in production)"

scripts/install/traefik-dynamic.yml

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+# Dynamic (file-provider) Traefik config for the OtOpcUa admin HTTP routing.
+# Picked up by traefik.yml's file provider (with watch: true) so router/service
+# edits hot-reload without a Traefik restart.
+
+http:
+  routers:
+    otopcua-admin:
+      entryPoints: ["web"]
+      rule: "HostRegexp(`otopcua.*`)"
+      service: otopcua-admin
+
+  services:
+    otopcua-admin:
+      loadBalancer:
+        servers:
+          - url: "http://admin-a:9000"
+          - url: "http://admin-b:9000"
+        healthCheck:
+          path: /health/active
+          interval: 5s
+          timeout: 2s
+          # Default expected status is 2xx. Followers return 503 from
+          # /health/active so Traefik will drop them from the balancer
+          # within the next interval after a leadership change.

scripts/install/traefik.yml

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+# Traefik static configuration for the OtOpcUa fleet HTTP front door.
+#
+# Routes admin-role HTTP traffic (Blazor + auth + SignalR + /auth/*) to whichever
+# OtOpcUa.Host node currently holds the admin role-leader. Uses the /health/active
+# endpoint as the active-leader signal: a node returns 200 only when it is the
+# Akka admin role-leader; followers return 503 and Traefik routes around them.
+#
+# OPC UA traffic is NOT routed through Traefik — clients connect directly to
+# opc.tcp://node:4840 on every driver node and use the standard ServiceLevel
+# heuristic for failover.
+
+entryPoints:
+  web:
+    address: ":80"
+
+providers:
+  file:
+    filename: /etc/traefik/dynamic.yml
+    watch: true
+
+api:
+  insecure: true
+  dashboard: true
+
+log:
+  level: INFO
+  format: common
+
+accessLog:
+  format: common