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>

bin/feynman.js

@@ -17,10 +17,15 @@ function compareNodeVersions(left, right) {
 }
 
 if (compareNodeVersions(parseNodeVersion(process.versions.node), parseNodeVersion(MIN_NODE_VERSION)) < 0) {
+  const isWindows = process.platform === "win32";
   console.error(`feynman requires Node.js ${MIN_NODE_VERSION} or later (detected ${process.versions.node}).`);
-  console.error("Switch to Node 20 with `nvm install 20 && nvm use 20`, or use the standalone installer:");
-  console.error("curl -fsSL https://feynman.is/install | bash");
+  console.error(isWindows
+    ? "Install a newer Node.js from https://nodejs.org, or use the standalone installer:"
+    : "Switch to Node 20 with `nvm install 20 && nvm use 20`, or use the standalone installer:");
+  console.error(isWindows
+    ? "irm https://feynman.is/install.ps1 | iex"
+    : "curl -fsSL https://feynman.is/install | bash");
   process.exit(1);
 }
-await import("../scripts/patch-embedded-pi.mjs");
-await import("../dist/index.js");
+await import(new URL("../scripts/patch-embedded-pi.mjs", import.meta.url).href);
+await import(new URL("../dist/index.js", import.meta.url).href);