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_runs.py

@@ -8,10 +8,10 @@ parameters a caller sends are refused before anything runs if they are wrong.
 
 import pytest
 
-from app.flow.messages import DType, MessageSpec
-from app.flow.nodes import Node
-from app.flow.pipeline import NodeOutcome, Pipeline
-from app.flow.runs import (
+from fluksio.flow.messages import DType, MessageSpec
+from fluksio.flow.nodes import Node
+from fluksio.flow.pipeline import NodeOutcome, Pipeline
+from fluksio.flow.runs import (
     MetricSink,
     RunRejected,
     batch_issues,
@@ -20,8 +20,8 @@ from app.flow.runs import (
     required_labels,
     seed_values,
 )
-from app.flow.schemas import FlowDef, FlowInput, NodeDef
-from app.flow.state import MemoryState
+from fluksio.flow.schemas import FlowDef, FlowInput, NodeDef
+from fluksio.flow.state import MemoryState
 
 
 def spec(name: str, dtype: DType = DType.FLOAT, **kwargs) -> MessageSpec: