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/alembic.ini

@@ -2,7 +2,7 @@
 
 [alembic]
 # path to migration scripts
-script_location = app/alembic
+script_location = fluksio/alembic
 
 # template used to generate migration files
 # file_template = %%(rev)s_%%(slug)s