Run node code on the venv Fluksio was installed into

The workflow this serves: make a venv, install what you work with, then `pip
install fluksio` into the same one. Building a second environment beside it
was exactly wrong — the packages the nodes need are already here, and the
Modules screen was asking for them a second time.

`NODE_VENV=auto` (the default) adopts that venv. It declines in the three
cases where adopting would be wrong: `managed` says otherwise, a managed venv
already exists and may hold packages somebody installed on purpose, or the
engine is not running from a venv at all. The images set `managed`, since the
venv in them holds the app and nothing of anybody else's.

An adopted venv is never written to. `uv pip sync` makes a venv hold exactly
the manifest, so pointed at somebody's own environment it uninstalls their
work and the engine with it — `sync()` refuses outright and `reconcile()`
returns before it can be called at startup, which is where that would have
happened first. The Modules screen lists what is installed and drops its
editor; `pip` is how that environment changes.

`fluksio serve` now names the interpreter node code runs on, which is the
thing a data scientist most needs to know at that moment. `fluksio-worker`
already defaulted `--python` to its own interpreter, so a GPU box works the
same way — that was only ever undocumented.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012ue1tkFWB1bcGy3aWhCKpU

docs/code/cli.md

@@ -205,6 +205,7 @@ directory. The ones you are most likely to touch:
 |---|---|---|
 | `DATA_DIR` | `~/.fluksio` via the CLI | everything below it derives from this |
 | `DATABASE_URL` | SQLite in the data dir | any SQLAlchemy URL |
+| `NODE_VENV` | `auto` | which interpreter node code runs on: `auto` adopts the venv Fluksio was installed into, `managed` builds one of its own, or name an interpreter |
 | `REDIS_HOST` | unset | flow state in Redis instead of memory; survives a restart |
 | `FRONTEND_HOST` | — | the address used in mails, OAuth metadata and panel links |
 | `ENVIRONMENT` | `local` | `production` closes the interactive API schema |

docs/code/nodes.md

@@ -182,6 +182,14 @@ flows. An install takes effect immediately; nothing restarts.
 
 ### Your own code as a package
 
+!!! tip "If Fluksio is installed in the venv you work in, skip this"
+
+    Node code then runs on that environment, so your project and everything it
+    imports are already importable — see
+    [Getting started: data science](../getting-started/data-science.md). What
+    follows is for a Fluksio with a venv of its own, which is what a container
+    always has.
+
 A manifest line can name a directory, so the project you already have is
 installable like any other dependency: