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.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/tests/flow/test_workers.py

@@ -7,10 +7,10 @@ from collections.abc import Iterator
 
 import pytest
 
-from app.flow.artifacts import ArtifactStore
-from app.flow.messages import DType, MessageSpec
-from app.flow.worker_main import ARTIFACT_DIR_ENV
-from app.flow.workers import NodeCancelled, NodeTimeout, PythonWorkerPool
+from fluksio.flow.artifacts import ArtifactStore
+from fluksio.flow.messages import DType, MessageSpec
+from fluksio.flow.worker_main import ARTIFACT_DIR_ENV
+from fluksio.flow.workers import NodeCancelled, NodeTimeout, PythonWorkerPool
 
 
 @pytest.fixture