feat: support pnpm v12 (#288)

* feat: support pnpm v12

Approve the pinned @pnpm/exe install script for npm 12, add pnpm 12 coverage across supported runner platforms, and clarify that action-setup remains supported alongside pnpm/setup.

* refactor: use pnpm 12 native bootstrap

Install the plain pnpm v12 package as the single native bootstrap, remove the legacy @pnpm/exe lockfile and runtime path, and retain the standalone input as a no-op for workflow compatibility.

* fix: keep bootstrap updates on pnpm 12

Handle npm's array-shaped view output and resolve only pnpm 12 distribution tags.

* fix: use native bootstrap only for pnpm 12

Route pnpm 12-only versions and ranges through the plain pnpm native package while preserving the existing Node and @pnpm/exe bootstrap paths for older releases.

* style: remove updater narrative comments

pnpm-lock.yaml

@@ -29,6 +29,9 @@ importers:
       expand-tilde:
         specifier: ^2.0.2
         version: 2.0.2
+      semver:
+        specifier: ^7.8.5
+        version: 7.8.5
       yaml:
         specifier: ^2.3.4
         version: 2.7.0
@@ -36,6 +39,9 @@ importers:
         specifier: ^3.22.4
         version: 3.24.1
     devDependencies:
+      '@types/semver':
+        specifier: ^7.8.0
+        version: 7.8.0
       esbuild:
         specifier: ^0.27.4
         version: 0.27.4
@@ -293,6 +299,9 @@ packages:
   '@types/node@22.19.11':
     resolution: {integrity: sha512-BH7YwL6rA93ReqeQS1c4bsPpcfOmJasG+Fkr6Y59q83f9M1WcBRHR2vM+P9eOisYRcN3ujQoiZY8uk5W+1WL8w==}
 
+  '@types/semver@7.8.0':
+    resolution: {integrity: sha512-1mAINjtQCXXeLkJ9ehXkwOcBpqtLxiVtKhpUf83DdRNdQKV0iXZpaHYqRr7nj+wvxuJzoAmAwXI+sCNMv1CzLQ==}
+
   '@typespec/ts-http-runtime@0.3.0':
     resolution: {integrity: sha512-sOx1PKSuFwnIl7z4RN0Ls7N9AQawmR9r66eI5rFCzLDIs8HTIYrIpH9QjYWoX0lkgGrkLxXhi4QnK7MizPRrIg==}
     engines: {node: '>=20.0.0'}
@@ -463,6 +472,11 @@ packages:
     resolution: {integrity: sha512-BR7VvDCVHO+q2xBEWskxS6DJE1qRnb7DxzUrogb71CWoSficBxYsiAGd+Kl0mmq/MprG9yArRkyrQxTO6XjMzA==}
     hasBin: true
 
+  semver@7.8.5:
+    resolution: {integrity: sha512-Y7/KDsb8LjooZpwaqGyulO6DQlksgCncchHGk+sZIY4SBvUocMBEFH5Ur1fI4dV+Jvl0w6cjvucaIi40puRioA==}
+    engines: {node: '>=10'}
+    hasBin: true
+
   strnum@2.1.1:
     resolution: {integrity: sha512-7ZvoFTiCnGxBtDqJ//Cu6fWtZtc7Y3x+QOirG15wztbdngGSkht27o2pyGWrVy0b4WAy3jbKmnoK6g5VlVNUUw==}
 
@@ -770,6 +784,8 @@ snapshots:
     dependencies:
       undici-types: 6.21.0
 
+  '@types/semver@7.8.0': {}
+
   '@typespec/ts-http-runtime@0.3.0':
     dependencies:
       http-proxy-agent: 7.0.2
@@ -957,6 +973,8 @@ snapshots:
 
   semver@6.3.1: {}
 
+  semver@7.8.5: {}
+
   strnum@2.1.1: {}
 
   tr46@0.0.3: {}