fix: harden cross-platform release builds

Skip direct POSIX entrypoint execution on Windows CI and prevent test-support modules from entering clean build or npm package output.

package.json

@@ -12,6 +12,7 @@
   },
   "files": [
     "dist",
+    "!dist/**/*.testSupport.*",
     "install.sh",
     "README.md",
     "LICENSE",
@@ -29,7 +30,7 @@
     "dev:server": "npm run dev:web",
     "dev:client": "vite --host 0.0.0.0",
     "dev:plugins": "node scripts/build-plugins.mjs --watch",
-    "build": "tsc -p tsconfig.build.json && npm run build:plugin-api && npm run build:plugins && vite build",
+    "build": "npm run clean && tsc -p tsconfig.build.json && npm run build:plugin-api && npm run build:plugins && vite build",
     "build:plugin-api": "tsc -p tsconfig.plugin-api.json",
     "build:plugins": "tsc -p tsconfig.plugins.json && node scripts/build-plugins.mjs",
     "capture:screenshots": "node scripts/capture-screenshots.mjs",
@@ -40,7 +41,7 @@
     "verify": "npm run typecheck && npm run lint && npm run knip && npm test",
     "start": "tsx src/server/index.ts",
     "start:sessiond": "tsx src/server/sessiond.ts",
-    "clean": "rm -rf dist",
+    "clean": "node -e \"require('node:fs').rmSync('dist', { recursive: true, force: true })\"",
     "prepack": "npm run build",
     "pack:dry": "npm pack --dry-run",
     "prepublishOnly": "npm run verify",