Claude/windows install compatibility tr di s (#3)

* Fix Windows PowerShell 5.1 compatibility in installer

Use $env:PROCESSOR_ARCHITECTURE for arch detection instead of
RuntimeInformation::OSArchitecture which may not be loaded in
every Windows PowerShell 5.1 session. Also fix null-reference
when user PATH environment variable is empty.

https://claude.ai/code/session_01VFiRDM2ZweyacXN5JneVoP

* Fix executable resolution and tar extraction on Windows

resolveExecutable() used `sh -lc "command -v ..."` which doesn't work
on Windows (no sh). Now uses `cmd /c where` on win32. Also make tar
workspace restoration tolerate symlink failures on Windows — .bin/
symlinks can't be created without Developer Mode, but the actual
package directories are extracted fine.

https://claude.ai/code/session_01VFiRDM2ZweyacXN5JneVoP

* Broad Windows compatibility fixes across the codebase

- runtime.ts: Use path.delimiter instead of hardcoded ":" for PATH
  construction — was completely broken on Windows
- executables.ts: Add Windows fallback paths for Chrome, Edge, Brave,
  and Pandoc in Program Files; skip macOS-only paths on win32
- node-version.ts, check-node-version.mjs, bin/feynman.js: Show
  Windows-appropriate install instructions (irm | iex, nodejs.org)
  instead of nvm/curl on win32
- preview.ts: Support winget for pandoc auto-install on Windows, and
  apt on Linux (was macOS/brew only)
- launch.ts: Catch unsupported signal errors on Windows
- README.md: Add Windows PowerShell commands alongside macOS/Linux
  for all install instructions

https://claude.ai/code/session_01VFiRDM2ZweyacXN5JneVoP

* fix: complete windows bootstrap hardening

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Advait Paliwal <advaitspaliwal@gmail.com>

website/public/install.ps1

@@ -73,12 +73,26 @@ function Resolve-ReleaseMetadata {
 }
 
 function Get-ArchSuffix {
-  $arch = [System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture
-  switch ($arch.ToString()) {
-    "X64" { return "x64" }
-    "Arm64" { return "arm64" }
-    default { throw "Unsupported architecture: $arch" }
+  # Prefer PROCESSOR_ARCHITECTURE which is always available on Windows.
+  # RuntimeInformation::OSArchitecture requires .NET 4.7.1+ and may not
+  # be loaded in every Windows PowerShell 5.1 session.
+  $envArch = $env:PROCESSOR_ARCHITECTURE
+  if ($envArch) {
+    switch ($envArch) {
+      "AMD64" { return "x64" }
+      "ARM64" { return "arm64" }
+    }
   }
+
+  try {
+    $arch = [System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture
+    switch ($arch.ToString()) {
+      "X64" { return "x64" }
+      "Arm64" { return "arm64" }
+    }
+  } catch {}
+
+  throw "Unsupported architecture: $envArch"
 }
 
 $archSuffix = Get-ArchSuffix
@@ -134,7 +148,11 @@ Workarounds:
 "@ | Set-Content -Path $shimPath -Encoding ASCII
 
   $currentUserPath = [Environment]::GetEnvironmentVariable("Path", "User")
-  if (-not $currentUserPath.Split(';').Contains($installBinDir)) {
+  $alreadyOnPath = $false
+  if ($currentUserPath) {
+    $alreadyOnPath = $currentUserPath.Split(';') -contains $installBinDir
+  }
+  if (-not $alreadyOnPath) {
     $updatedPath = if ([string]::IsNullOrWhiteSpace($currentUserPath)) {
       $installBinDir
     } else {