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_library.py

@@ -4,9 +4,9 @@ from pathlib import Path
 
 import pytest
 
-from app.flow.messages import MessageSpec
-from app.flow.schemas import FlowDef, NodeDef
-from app.flow.store import FlowStore, LibExists, LibNotFound
+from fluksio.flow.messages import MessageSpec
+from fluksio.flow.schemas import FlowDef, NodeDef
+from fluksio.flow.store import FlowStore, LibExists, LibNotFound
 
 SOURCE = "def process():\n    return {'temp': 1}\n"