Add local PowerShell CI check script

scripts/ci-local.ps1

@@ -0,0 +1,67 @@
+param(
+    [switch]$SkipNpmInstall,
+    [switch]$SkipDotnetRestore,
+    [switch]$SkipBuild
+)
+
+Set-StrictMode -Version Latest
+$ErrorActionPreference = "Stop"
+
+function Invoke-Step {
+    param(
+        [Parameter(Mandatory = $true)][string]$Name,
+        [Parameter(Mandatory = $true)][scriptblock]$Action
+    )
+
+    Write-Host "==> $Name"
+    & $Action
+    if ($LASTEXITCODE -ne 0) {
+        throw "Step failed: $Name"
+    }
+}
+
+$scriptDir = Split-Path -Parent $MyInvocation.MyCommand.Path
+$repoRoot = Split-Path -Parent $scriptDir
+
+Push-Location $repoRoot
+try {
+    if (-not $SkipNpmInstall) {
+        Invoke-Step -Name "Install frontend tooling (npm install)" -Action {
+            npm install
+        }
+    }
+
+    Invoke-Step -Name "Lint frontend" -Action {
+        npm run lint
+    }
+
+    Invoke-Step -Name "Check frontend formatting" -Action {
+        npm run format:check
+    }
+
+    if (-not $SkipDotnetRestore) {
+        Invoke-Step -Name "Restore .NET solution" -Action {
+            dotnet restore GameList.sln
+        }
+    }
+
+    if (-not $SkipBuild) {
+        Invoke-Step -Name "Build .NET solution (warnings as errors)" -Action {
+            dotnet build GameList.sln --no-restore -warnaserror
+        }
+    }
+
+    Invoke-Step -Name "Run tests" -Action {
+        if ($SkipBuild) {
+            dotnet test GameList.Tests/GameList.Tests.csproj --verbosity normal
+        }
+        else {
+            dotnet test GameList.Tests/GameList.Tests.csproj --no-build --verbosity normal
+        }
+    }
+
+    Write-Host "CI checks passed."
+}
+finally {
+    Pop-Location
+}