fix(ci): staging script was CommonJS in an ES-module package

ostp-gui/package.json sets "type": "module", so a .js file is loaded as an ES
module and `require` is not defined — the installer build died on the first
line of stage-sidecar.js. Renamed to .cjs, which opts that one file back into
CommonJS.

The failure was also reported in the wrong place. pwsh does not abort a run
block when a native command exits non-zero, so the build carried on past the
dead script and failed several steps later complaining about a sidecar that
nothing had staged. The two commands are chained now, so staging failures
surface as themselves.

Verified locally this time: the script resolves the host triple, copies the
helper to the name Tauri expects, and warns about a missing wintun.dll rather
than failing silently.

.github/workflows/release.yml

@@ -426,9 +426,10 @@ jobs:
       # first, and fail the build script when it is not.
       - name: Build NSIS Installer
         working-directory: ostp-gui
-        run: |
-          node stage-sidecar.js --release --target ${{ matrix.target }}
-          npx tauri build --bundles nsis --target ${{ matrix.target }} --config src-tauri/tauri.installer.conf.json
+        # Chained, not two lines: pwsh does not abort a run block when a native
+        # command fails, so a staging failure would otherwise be reported far
+        # downstream as a missing sidecar rather than as itself.
+        run: node stage-sidecar.cjs --release --target ${{ matrix.target }} && npx tauri build --bundles nsis --target ${{ matrix.target }} --config src-tauri/tauri.installer.conf.json
 
       - name: Collect installer
         shell: pwsh

ostp-gui/package.json

@@ -7,9 +7,9 @@
     "tauri": "tauri",
     "dev": "cargo build -p ostp-tun-helper && npx tauri dev",
     "build": "cargo build -p ostp-tun-helper --release && npx tauri build --no-bundle",
-    "build:installer": "cargo build -p ostp-tun-helper --release && node stage-sidecar.js --release && npx tauri build --bundles nsis --config src-tauri/tauri.installer.conf.json",
+    "build:installer": "cargo build -p ostp-tun-helper --release && node stage-sidecar.cjs --release && npx tauri build --bundles nsis --config src-tauri/tauri.installer.conf.json",
     "build:dist": "npm run build && node build_dist.js",
-    "sidecar": "node stage-sidecar.js"
+    "sidecar": "node stage-sidecar.cjs"
   },
   "devDependencies": {
     "@tauri-apps/cli": "^2"