fix(install): require Node >=20.19/22.12 for the desktop build

The "Build desktop app" install step failed with an opaque "exit code 1"
on machines with an old Node, and nothing in the logs explained it.

Reproduced: on Node 20.5.1, `npm run pack`'s `vite build` crashes with

  You are using Node.js 20.5.1. Vite requires Node.js version 20.19+ or 22.12+.
  SyntaxError: The requested module 'node:util' does not provide an
  export named 'styleText'

Vite 8 (rolldown) imports node:util.styleText, which doesn't exist before
Node 20.12, so the build dies before producing the app. The installer's
check_node / Test-Node accepted ANY pre-existing Node with no version
floor, so a too-old system Node was used for the build instead of the
bundled Node 22.

Add a version floor (^20.19 || >=22.12) to check_node (install.sh) and
Test-Node (install.ps1): a too-old system Node is replaced with the
Hermes-managed Node 22 LTS, and the desktop stage re-resolves Node so the
build always runs on a satisfying version. Declare the same range in
apps/desktop/package.json engines.

Verified: build succeeds on Node 22, fails on 20.5.1 with the error above;
the floor logic matches Vite's range across boundary versions (20.18/20.19,
21.x, 22.11/22.12).

scripts/install.ps1

@@ -714,19 +714,39 @@ function Set-GitBashEnvVar {
     Write-Info "If needed, set HERMES_GIT_BASH_PATH manually to your bash.exe path."
 }
 
+# The desktop build runs Vite ^8, which refuses to start on Node outside
+# `^20.19 || >=22.12` -- older Node lacks node:util.styleText, so `vite build`
+# crashes with a SyntaxError that surfaces only as the opaque "Build desktop
+# app ... exit code 1" install failure. Returns $true when a `node --version`
+# string clears that floor.
+function Test-NodeVersionOk {
+    param([string]$Version)
+    try {
+        $v = [version]($Version -replace '^v', '' -replace '-.*$', '')
+    } catch {
+        return $false
+    }
+    if ($v.Major -eq 20 -and $v.Minor -ge 19) { return $true }
+    if ($v.Major -ge 22 -and ($v.Major -gt 22 -or $v.Minor -ge 12)) { return $true }
+    return $false
+}
+
 function Test-Node {
     Write-Info "Checking Node.js (for browser tools)..."
 
     if (Get-Command node -ErrorAction SilentlyContinue) {
         $version = node --version
-        Write-Success "Node.js $version found"
-        $script:HasNode = $true
-        return $true
+        if (Test-NodeVersionOk $version) {
+            Write-Success "Node.js $version found"
+            $script:HasNode = $true
+            return $true
+        }
+        Write-Warn "Node.js $version is too old for the desktop build (need ^20.19 or >=22.12)"
     }
 
-    # Check our own managed install from a previous run
+    # Prefer a Hermes-managed Node from a previous run over a too-old system one.
     $managedNode = "$HermesHome\node\node.exe"
-    if (Test-Path $managedNode) {
+    if ((Test-Path $managedNode) -and (Test-NodeVersionOk (& $managedNode --version))) {
         $version = & $managedNode --version
         $env:Path = "$HermesHome\node;$env:Path"
         Write-Success "Node.js $version found (Hermes-managed)"
@@ -734,7 +754,7 @@ function Test-Node {
         return $true
     }
 
-    Write-Info "Node.js not found -- installing Node.js $NodeVersion LTS..."
+    Write-Info "Installing Hermes-managed Node.js $NodeVersion LTS..."
 
     # Try the portable-zip path FIRST -- no UAC, no admin, no winget MSI.
     # winget install OpenJS.NodeJS.LTS triggers a system-wide MSI install
@@ -1906,16 +1926,17 @@ function Install-Desktop {
     # so an "unpacked" build (electron-builder --dir) is enough — we
     # don't need to produce an NSIS/MSI artifact here.
 
-    if (-not $HasNode) {
-        # Cross-process driver mode: each `-Stage NAME` invocation runs in a
-        # fresh PowerShell process, so $script:HasNode set by Stage-Node
-        # in the previous process isn't visible. Re-detect rather than
-        # trusting the global.
-        if (-not (Get-Command npm -ErrorAction SilentlyContinue)) {
-            Write-Warn "Skipping desktop build (Node.js / npm not on PATH)"
-            $script:_StageSkippedReason = "Node.js not available"
-            return
-        }
+    # Always re-resolve Node here. Stages run in separate PowerShell processes,
+    # so $script:HasNode from Stage-Node isn't visible; more importantly Test-Node
+    # enforces the build floor (^20.19 || >=22.12) and prepends the Hermes-managed
+    # Node to PATH, so the build never runs on a too-old system Node -- the cause
+    # of the opaque "Build desktop app ... exit code 1" failure (Vite crashes on
+    # old Node).
+    Test-Node | Out-Null
+    if (-not (Get-Command npm -ErrorAction SilentlyContinue)) {
+        Write-Warn "Skipping desktop build (Node.js / npm not on PATH)"
+        $script:_StageSkippedReason = "Node.js not available"
+        return
     }
 
     $desktopDir = "$InstallDir\apps\desktop"