One image for the whole app: engine, API and dashboard on one port

The backend image now builds the SPA and serves it on the API's own origin
(fluksio/spa.py), so an instance is a single container with no proxy, DNS,
port 80 or .env: `docker compose up -d` with the new compose.yml runs it on
localhost:8080. It starts on fluksio serve (persisted secret key, first
admin printed once) and brings its own Redis when REDIS_HOST is unset.

Slimmer: python:3.13-slim, no dev group, uv once, fastapi without the cloud
CLI. Optional features are per-feature extras (mqtt, influx, email, sentry,
ml, server for all) picked with the EXTRAS build argument; numpy moved to
`ml`. ffmpeg left the image for imageio-ffmpeg via the Modules screen.

The operator stack runs the same image with app. and api. routed to it; the
nginx frontend service, the LAN nginx proxy and DOMAIN in the backend are
gone, and the MCP issuer is FRONTEND_HOST.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/code/nodes.md

@@ -144,6 +144,7 @@ import subprocess
 import tempfile
 
 import fluksio
+import imageio_ffmpeg
 
 # H.264 Constrained Baseline, at most 640x360 and 15 fps, mono AAC.
 PANEL = [
@@ -157,10 +158,11 @@ PANEL = [
 
 def process(clip):
     source = fluksio.load_artifact(clip)
+    ffmpeg = imageio_ffmpeg.get_ffmpeg_exe()
     with tempfile.TemporaryDirectory() as tmp:
         target = os.path.join(tmp, "panel.mp4")
         subprocess.run(
-            ["ffmpeg", "-nostdin", "-loglevel", "error", "-i", source, *PANEL, target],
+            [ffmpeg, "-nostdin", "-loglevel", "error", "-i", source, *PANEL, target],
             check=True,
             timeout=600,
         )
@@ -169,10 +171,9 @@ def process(clip):
 ```
 
 Use it only for clips headed for such a panel. Browsers play the originals,
-and the result plays there too, just smaller. The node needs `ffmpeg` on the
-`PATH`. The Docker image includes it only when built with
-[`WITH_FFMPEG=true`](../reference/configuration.md#image-options) in `.env`.
-Otherwise run the node on a [remote worker](workers.md) that has it.
+and the result plays there too, just smaller. Add `imageio-ffmpeg` on the
+**Modules** screen first. It brings a static `ffmpeg` build for Linux on x86
+and ARM, so nothing has to be installed into the image.
 
 ### Speech to and from a panel