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/api/routes/test_flows.py

@@ -4,8 +4,8 @@ from fastapi.testclient import TestClient
 from sqlalchemy import func
 from sqlmodel import Session, select
 
-from app.core.config import settings
-from app.models import Run, RunArtifact, RunMetric, RunNode
+from fluksio.core.config import settings
+from fluksio.models import Run, RunArtifact, RunMetric, RunNode
 
 PREFIX = f"{settings.API_V1_STR}/flows"