fix(electron): simplify production load and CI frontend build

Remove unused url.format import and switch from loadURL with a
formatted file: URL to loadFile for production. This simplifies code,
avoids manual file URL construction, and makes the production path
loading more robust.
Also update CI job to build the frontend via the NX command
(npx nx build web --skip-nx-cache) instead of npm run build:frontend,
aligning the workflow with the monorepo's canonical build command.

.github/workflows/build-and-make.yaml

@@ -41,7 +41,7 @@ jobs:
               run: pnpm install --no-frozen-lockfile
 
             - name: Build frontend
-              run: npm run build:frontend
+              run: npx nx build web --skip-nx-cache
 
             - name: Build backend
               run: npm run build:backend