ci(release-stable): install NSIS on win runner before electron-builder

The win build job was failing with `makensis is required to build the
Windows installer; install NSIS or populate the electron-builder NSIS
cache` because GitHub's windows-latest runner image no longer ships
NSIS by default and `tools-pack`'s `resolveMakensisCommand` throws
when it cannot find `makensis.exe`.

The matching fix already exists in release-beta.yml (added in #768).
Mirror that step into release-stable.yml so the stable release lane
can build the win NSIS installer too.

Workflow-only change. Does not affect the packaged app contents
shipped from this commit (release artifacts are byte-identical to
what release-beta produced from 4761906).

.github/workflows/release-stable.yml

@@ -237,6 +237,14 @@ jobs:
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
 
+      - name: Setup NSIS
+        shell: pwsh
+        run: |
+          if ((Get-Command makensis.exe -ErrorAction SilentlyContinue) -or (Test-Path "C:\Program Files (x86)\NSIS\makensis.exe")) {
+            exit 0
+          }
+          choco install nsis -y --no-progress
+
       - name: Build stable windows artifacts
         shell: pwsh
         run: >-