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_supervision.py

@@ -4,9 +4,9 @@ import asyncio
 
 import pytest
 
-from app.flow import supervision
-from app.flow.events import EventBus
-from app.flow.supervision import FAILURE_BUDGET, Supervisor
+from fluksio.flow import supervision
+from fluksio.flow.events import EventBus
+from fluksio.flow.supervision import FAILURE_BUDGET, Supervisor
 
 
 @pytest.fixture(autouse=True)