chore: align packageManager and engines fields across repos

- Change packageManager to exact version: pnpm@10.21.0 (Corepack requires exact semver)
- Update engines.pnpm from >=10.16.0 to >=10.21.0 (align with other repos)
- engines.node already consistent at >=18

Author: jdalton

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@socketsecurity/sdk",
   "version": "3.1.3",
-  "packageManager": "pnpm@>=10.21.0",
+  "packageManager": "pnpm@10.21.0",
   "license": "MIT",
   "description": "SDK for the Socket API client",
   "author": {
@@ -105,7 +105,7 @@
   },
   "engines": {
     "node": ">=18",
-    "pnpm": ">=10.16.0"
+    "pnpm": ">=10.21.0"
   },
   "files": [
     "CHANGELOG.md",