One app fixture for the tests, and ViewModels built where they are used

The tests' `app` fixture, the same two lines in eleven files, now lives once in
tests/conftest.py.

On Android each ViewModel carried a companion `factory` that only wrapped its
constructor in viewModelFactory { initializer { … } }. MainActivity now builds
each one with Compose's viewModel { … } builder, so the five factories and their
imports are gone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_sync.py

@@ -1,8 +1,5 @@
 from datetime import datetime, timezone
 
-import pytest
-
-from inkwell.app import create_app
 from inkwell.sync import (
     DEFAULT_LIMIT,
     MAX_LIMIT,
@@ -17,11 +14,6 @@ from inkwell.sync import (
 )
 
 
-@pytest.fixture
-def app():
-    return create_app()
-
-
 async def test_changes_requires_auth(app):
     client = app.test_client()
     resp = await client.get("/api/sync/changes")