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>

development.md

@@ -66,7 +66,7 @@ Standalone (`cd app && make dev`) publishes the full set:
 
 ## Hot reload, and what it misses
 
-`compose.dev.yml` bind-mounts `backend/app` into the api container and runs uvicorn with
+`compose.dev.yml` bind-mounts `backend/fluksio` into the api container and runs uvicorn with
 `--reload`, so a backend edit is live. The `develop.watch` block next to it syncs the same
 directory, but only under `docker compose watch`, which no target runs — the detached
 `up -d` flow never triggers it. The mount is what does the work, so an api container created