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.

.github/workflows/test.yaml

@@ -33,7 +33,14 @@ jobs:
         run: which pnpm; which pnpx
 
       - name: 'Test: version'
-        run: pnpm --version
+        run: |
+          actual="$(pnpm --version)"
+          echo "pnpm version: ${actual}"
+          if [[ ! "${actual}" =~ ^[0-9]+\.[0-9]+\.[0-9]+(-.+)?$ ]]; then
+            echo "ERROR: pnpm --version did not produce valid output"
+            exit 1
+          fi
+        shell: bash
 
       - name: 'Test: install in a fresh project'
         run: |
@@ -71,7 +78,14 @@ jobs:
         run: which pnpm && which pnpx
 
       - name: 'Test: version'
-        run: pnpm --version
+        run: |
+          actual="$(pnpm --version)"
+          echo "pnpm version: ${actual}"
+          if [[ ! "${actual}" =~ ^[0-9]+\.[0-9]+\.[0-9]+(-.+)?$ ]]; then
+            echo "ERROR: pnpm --version did not produce valid output"
+            exit 1
+          fi
+        shell: bash
 
   test_standalone:
     name: Test with standalone
@@ -98,7 +112,14 @@ jobs:
         run: which pnpm
 
       - name: 'Test: version'
-        run: pnpm --version
+        run: |
+          actual="$(pnpm --version)"
+          echo "pnpm version: ${actual}"
+          if [[ ! "${actual}" =~ ^[0-9]+\.[0-9]+\.[0-9]+(-.+)?$ ]]; then
+            echo "ERROR: pnpm --version did not produce valid output"
+            exit 1
+          fi
+        shell: bash
 
       - name: 'Test: install in a fresh project'
         run: |
@@ -196,4 +217,11 @@ jobs:
         run: which pnpm; which pnpx
 
       - name: 'Test: version'
-        run: pnpm --version
+        run: |
+          actual="$(pnpm --version)"
+          echo "pnpm version: ${actual}"
+          if [[ ! "${actual}" =~ ^[0-9]+\.[0-9]+\.[0-9]+(-.+)?$ ]]; then
+            echo "ERROR: pnpm --version did not produce valid output"
+            exit 1
+          fi
+        shell: bash