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_notes.py

@@ -5,7 +5,6 @@ from datetime import datetime, timezone
 
 import pytest
 
-from inkwell.app import create_app
 from inkwell.common import coerce_bool, parse_dt
 from inkwell.colors import NOTE_COLORS
 from inkwell.models.note import Note
@@ -34,11 +33,6 @@ from inkwell.notes.recurrence import next_occurrence, normalize_recurrence
 from inkwell.notes.tags import parse_tags, split_body_tags
 
 
-@pytest.fixture
-def app():
-    return create_app()
-
-
 def test_all_note_routes_registered(app):
     # Guards the notes package split: every route handler must still be attached to the
     # blueprint. A route whose module isn't imported by notes/__init__ would silently