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_queue.py

@@ -2,12 +2,12 @@
 
 import time
 
-from app.flow.executor import ExecutionService
-from app.flow.messages import DType, MessageSpec
-from app.flow.nodes import Node
-from app.flow.pipeline import Pipeline
-from app.flow.queue import MemoryWorkQueue, WorkItem
-from app.flow.state import MemoryState
+from fluksio.flow.executor import ExecutionService
+from fluksio.flow.messages import DType, MessageSpec
+from fluksio.flow.nodes import Node
+from fluksio.flow.pipeline import Pipeline
+from fluksio.flow.queue import MemoryWorkQueue, WorkItem
+from fluksio.flow.state import MemoryState
 
 
 def test_items_come_back_in_the_order_they_went_in():