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_watchdog.py

@@ -2,9 +2,9 @@
 
 from fastapi.testclient import TestClient
 
-from app.flow.events import EventBus
-from app.flow.watchdog import DEGRADED_STRIKES, LoopWatchdog
-from app.main import app
+from fluksio.flow.events import EventBus
+from fluksio.flow.watchdog import DEGRADED_STRIKES, LoopWatchdog
+from fluksio.main import app
 
 
 def test_a_responsive_loop_stays_healthy():