fix: move ajv to dependencies and auto-install deps in install scripts

`ajv` is required at runtime by the installer (`scripts/lib/install/config.js`)
but was listed under `devDependencies`. This caused `Error: Cannot find module
'ajv'` when running `./install.sh` from a fresh git clone or via `npx`.

- Move `ajv` from devDependencies to dependencies in package.json
- Add auto `npm install` in install.sh when node_modules is missing
- Add matching auto-install in install.ps1 for Windows parity

install.ps1

@@ -34,5 +34,14 @@ while ($true) {
 $scriptDir = Split-Path -Parent $scriptPath
 $installerScript = Join-Path -Path (Join-Path -Path $scriptDir -ChildPath 'scripts') -ChildPath 'install-apply.js'
 
+# Auto-install Node dependencies when running from a git clone
+$nodeModules = Join-Path -Path $scriptDir -ChildPath 'node_modules'
+if (-not (Test-Path -LiteralPath $nodeModules)) {
+    Write-Host '[ECC] Installing dependencies...'
+    Push-Location $scriptDir
+    try { & npm install --no-audit --no-fund --loglevel=error }
+    finally { Pop-Location }
+}
+
 & node $installerScript @args
 exit $LASTEXITCODE