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/fluksio/flow/__init__.py

@@ -0,0 +1,26 @@
+"""The flow engine: nodes, the pipeline that runs them, and their storage."""
+
+from fluksio.flow.controller import FlowController, NodeStatus
+from fluksio.flow.events import EventBus, event_bus
+from fluksio.flow.messages import DType, MessageSpec, qualify
+from fluksio.flow.nodes import Node
+from fluksio.flow.pipeline import Pipeline, ValidationIssue
+from fluksio.flow.state import MemoryState, RedisState, StateBackend
+from fluksio.flow.store import FlowStore
+
+__all__ = [
+    "DType",
+    "EventBus",
+    "FlowController",
+    "FlowStore",
+    "MemoryState",
+    "MessageSpec",
+    "Node",
+    "NodeStatus",
+    "Pipeline",
+    "RedisState",
+    "StateBackend",
+    "ValidationIssue",
+    "event_bus",
+    "qualify",
+]