Fix demo login credentials and form encoding

backend/app/main.py

@@ -1,9 +1,9 @@
 from fastapi import FastAPI
 from app.routes.auth import router as auth_router
 
-app = FastAPI(title='NetMapper API')
+app = FastAPI(title="NetMapper API")
 app.include_router(auth_router)
 
-@app.get('/health')
+@app.get("/health")
 async def health():
-    return {'status': 'ok'}
+    return {"status": "ok"}