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>

docker/compose.dev.yml

@@ -93,7 +93,7 @@ services:
       - fastapi
       - run
       - --reload
-      - "app/main.py"
+      - "fluksio/main.py"
     develop:
       watch:
         - path: ../backend
@@ -109,7 +109,7 @@ services:
       # `make dev-local`): it starts the stack with `up -d`, which never runs the
       # sync above — only `docker compose watch` does. Without the mount the
       # container serves the source baked into the image until it is rebuilt.
-      - ../backend/app:/app/backend/app
+      - ../backend/fluksio:/app/backend/fluksio
     environment:
       SMTP_HOST: "mailcatcher"
       SMTP_PORT: "1025"