Rename the import package app to fluksio

A wheel whose top-level module is `app` collides with anything else in a
user's venv, so the package that is about to be published takes the name
it is published under. Only the Python package moves; the repo, the
Docker WORKDIR and the compose project keep theirs.

backend/tests/flow/test_modules.py

@@ -6,8 +6,8 @@ from pathlib import Path
 
 import pytest
 
-from app.flow import modules
-from app.flow.store import FlowStore
+from fluksio.flow import modules
+from fluksio.flow.store import FlowStore
 
 pytestmark = pytest.mark.skipif(
     shutil.which("uv") is None, reason="module management needs uv"