Add the fluksio CLI: serve, enroll, worker

`pip install fluksio && fluksio serve` on a machine with no Docker, no
database and no configuration — which is the case this is for: a node on
a cluster where ports cannot be opened. It makes its data directory, its
key and an admin account, prints the password once, and serves. Pairing
is `fluksio enroll <code> --portal …`, doing what the Settings screen
does through the same function, before the engine starts and without one
running — a machine nobody can route to has no browser pointed at it
either. The portal serves the dashboard, so nothing is served here.

Two things had to give way. `fastapi[standard]` pulls a cloud CLI that
wants sentry-sdk 2.x while we pinned below it — no pip resolution
existed, so the pin is lifted, which the comment beside it had been
waiting for and which also lets the Python cap go. And `uv` is now a
dependency rather than something to find on PATH: the Modules screen is
how a data scientist installs torch, and it was quietly falling back to
the engine's own interpreter.

The CLI imports nothing from the engine before it has set DATA_DIR — the
settings are built on the first import of core.config, and reaching it
early put the database in the working directory. There is a test for
that now, because the failure is silent.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/fluksio/cloud/connector.py

@@ -27,8 +27,8 @@ from typing import Any
 import httpx
 from fastapi import FastAPI
 
+import fluksio
 from fluksio.cloud import config as cloud_config
-from fluksio.core.config import settings
 
 logger = logging.getLogger(__name__)
 
@@ -443,4 +443,4 @@ def _query_value(query: str, key: str) -> str:
 
 
 def _version() -> str:
-    return settings.VERSION if hasattr(settings, "VERSION") else "0.1.0"
+    return fluksio.__version__