fix: build @fusion/core and @fusion/engine dist in desktop packaging

The packaged desktop "Local" runtime dynamically imports @fusion/engine, whose
tsc dist is gitignored. desktop-windows.yml built only `@fusion/desktop build`
(no root `pnpm build`), so it packaged an empty engine/dist and the app crashed
on Local mode with ERR_MODULE_NOT_FOUND for app.asar/node_modules/@fusion/engine.

Make the desktop build self-contained (build core then engine before packaging)
and add the parity `pnpm build` step to desktop-windows.yml.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/desktop-windows.yml

@@ -22,6 +22,16 @@ jobs:
       - name: Install dependencies
         run: pnpm install --frozen-lockfile
 
+      # FNXC:WindowsDesktopPackaging 2026-07-01-19:45:
+      # Mirror release.yml: build every workspace package's tsc dist (incl.
+      # @fusion/core and @fusion/engine, which are gitignored) before packaging.
+      # Without this the embedded Local runtime's `import("@fusion/engine")`
+      # resolves to an empty dist and the app crashes with ERR_MODULE_NOT_FOUND.
+      # `@fusion/desktop build` now also self-builds these, so this is belt-and-
+      # suspenders parity that additionally covers any other workspace runtime dep.
+      - name: Build workspace
+        run: pnpm build
+
       - name: Build desktop package
         run: pnpm --filter @fusion/desktop build