test(CLI): Update test template to use create_app_fixture

[karangattu]

Replaces the use of local_app with app for ShinyAppProc. This improves consistency and aligns with updated testing practices.

So now when the user runs shiny add test and the app dir is accordion/app_express.py
if the user chooses the tests to be created as accordion/tests/test_app.py
the created file will look like this

from playwright.sync_api import Page

from shiny.playwright import controller
from shiny.pytest import create_app_fixture
from shiny.run import ShinyAppProc

app = create_app_fixture("../app-express.py")


def test_accordion_demo1(page: Page, app: ShinyAppProc) -> None:
    page.goto(app.url)

Else if the user chooses the tests to be created as accordion/test_app.py i.e. living besides the app_express.py file, the created file will look like this

from playwright.sync_api import Page

from shiny.playwright import controller
from shiny.pytest import create_app_fixture
from shiny.run import ShinyAppProc

app = create_app_fixture("app-express.py")


def test_accordion_demo1(page: Page, app: ShinyAppProc) -> None:

[schloerke]

Note: Advanced users can still use local_app test fixture.