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/reference/node-types.md

@@ -6,9 +6,9 @@ settings in the node panel; use a **Function** node for your own Python.
 `GET /flows/node-types` returns this list with each type's full parameter
 schema, including any [connectors](#connectors) installed on your instance.
 
-MQTT and InfluxDB need `pip install 'fluksio[server]'` on a Python installation.
-The Docker image includes these dependencies. Run the broker and database
-separately, or use the development stack's test services.
+MQTT and InfluxDB need their [extras](configuration.md#image-options): `mqtt`
+and `influx` in the image's `EXTRAS`, or `pip install 'fluksio[mqtt,influx]'`
+on a Python installation. Run the broker and database separately.
 
 ## Function