fix: Windows standalone mode — bypass broken npm shims (#217)

* fix: overwrite npm .cmd wrappers for @pnpm/exe on Windows

npm creates .cmd wrappers that invoke bin entries through `node`,
but @pnpm/exe bins are native executables, not JavaScript files.
This causes pnpm commands to silently fail on Windows.

* fix: copy pnpm.exe to .bin/ on Windows for standalone mode

The .cmd wrapper approach didn't work because CMD doesn't properly
wait for extensionless PE binaries. Instead, copy the actual .exe
(and .cmd for pnpx) from @pnpm/exe into .bin/ so PATHEXT finds
pnpm.exe directly, bypassing npm's broken node-wrapping shim.

* fix: add @pnpm/exe dir to PATH on Windows instead of .bin shims

On Windows, npm's .bin shims can't properly execute the extensionless
native binaries from @pnpm/exe. Instead of trying to fix the shims,
add the @pnpm/exe directory directly to PATH where pnpm.exe lives.

* test: validate pnpm --version output in CI

All version checks now capture output and assert it matches a semver
pattern. Previously, a silently failing pnpm (exit 0, no output)
would pass the tests.

* debug: log pnpm --version output during setup

* fix: remove duplicate addPath in setOutputs that shadowed pnpm.exe

setOutputs called addPath(node_modules/.bin) AFTER installPnpm had
already added the correct path (@pnpm/exe on Windows). Since
GITHUB_PATH entries are prepended, .bin ended up first in PATH,
causing PowerShell to find npm's broken shims instead of pnpm.exe.

* fix: add PNPM_HOME/bin to PATH on all platforms

* fix: address review feedback — PATH ordering and regex anchoring

- Swap addPath order so pnpmHome (with pnpm.exe) is prepended last
  and has highest precedence over pnpmHome/bin.
- Anchor version regex with $ and allow prerelease suffixes.

src/outputs/index.ts

@@ -1,10 +1,11 @@
-import { setOutput, addPath } from '@actions/core'
+import { setOutput } from '@actions/core'
 import { Inputs } from '../inputs'
 import { getBinDest } from '../utils'
 
 export function setOutputs(inputs: Inputs) {
   const binDest = getBinDest(inputs)
-  addPath(binDest)
+  // NOTE: addPath is already called in installPnpm — do not call it again
+  // here, as a second addPath would shadow the correct entry on Windows.
   setOutput('dest', inputs.dest)
   setOutput('bin_dest', binDest)
 }