fix(build): exclude *.test-helpers.ts from the electron-backend app tsconfig

The new operations.test-helpers.ts uses jest globals and broke the webpack
build and tsc typecheck, which compile every non-spec file in the app.
Exclude the test-helpers pattern alongside the existing spec exclusions.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/electron-backend/tsconfig.app.json

@@ -9,10 +9,12 @@
         "**/*.spec.ts",
         "**/*.spec-data.ts",
         "**/*.test.ts",
+        "**/*.test-helpers.ts",
         "jest.config.ts",
         "src/**/*.spec.ts",
         "src/**/*.spec-data.ts",
-        "src/**/*.test.ts"
+        "src/**/*.test.ts",
+        "src/**/*.test-helpers.ts"
     ],
     "include": ["**/*.ts"]
 }