fix: [carbone-ee] enable Studio and template management

The charm had no ``hooks/init``, so Carbone started in its default
stateless mode: no Studio, no template management, and ``CARBONE_BIND``
defaulting to ``127.0.0.1`` (unreachable behind the web-proxy).

Add ``hooks/init`` to:
- bind on ``0.0.0.0`` so the ``web-proxy`` can reach the service ;
- serve the Studio and ``/carbone-studio.js`` (``CARBONE_STUDIO``) ;
- enable stateful template management (``CARBONE_TEMPLATE_MANAGEMENT``):
  stable 64-bit template IDs, versioning and the ``/template`` endpoints ;
- align the datastore/configstore ownership on the unprivileged
  ``carbone`` image user, otherwise the container crash-loops with
  ``EACCES`` on ``/app/config/config.json``.

Persist ``/app/config`` as a ``config-resources`` and set a
``docker-compose.stop_grace_period`` of 200s: Carbone flushes its
template metadata on graceful shutdown, and Docker's 10s default would
SIGKILL it and lose templates on redeploy.  Flush metadata every
5 minutes to shrink the hard-crash window.

Bump the image to ``full-5.15.1`` and add a local ``basic-deploy`` test.

Verified locally: ``/status`` 200, ``/carbone-studio.js`` 200,
``GET /templates`` 200, template upload with versioning plus render
from the stable template ID, and metadata survival across a container
recreation.

carbone/README.org

@@ -4,14 +4,63 @@
 
 From: Carbone https://hub.docker.com/r/carbone/carbone-ee#running-carbone-community-edition-forever-free
 
-## Usage : 
+Upstream documentation:
+- On-premise configuration: https://carbone.io/documentation/developer/on-premise-installation/configuration.html
+- Template management: https://carbone.io/documentation/developer/on-premise-installation/template-management.html
+- Studio Web Component: https://carbone.io/documentation/developer/embedding/studio-web-component.html
+
+* What this charm enables
+
+By default Carbone starts in the *stateless* mode: it only renders the
+template sent with each request, exposes no Studio and keeps no template
+metadata.  The =init= hook turns it into the *stateful* service, which is
+what the charm is meant to provide:
+
+- =CARBONE_STUDIO=true= serves the Studio web interface and the
+  =/carbone-studio.js= Web Component.
+- =CARBONE_TEMPLATE_MANAGEMENT=true= enables stable 64-bit template IDs,
+  versioning, the =GET/POST/PATCH /template= endpoints and the
+  =embedded-versioning= Studio mode.
+- =CARBONE_BIND=0.0.0.0= makes Carbone listen on all interfaces so the
+  =web-proxy= can reach it (the upstream default is =127.0.0.1=).
+
+* Usage
 
 ex :
 
-```
+#+begin_src yaml
 carbone:
   relations:
     web-proxy:
       frontend:
         domain: carbone.dev1.elabore.coop
-```
+#+end_src
+
+* Persistence
+
+| Path            | Resource type    | Content                                              |
+|-----------------+------------------+------------------------------------------------------|
+| =/app/template= | =data-resources= | Templates and the metadata store (metadata.db)       |
+| =/app/config=   | =config-resources= | Optional license, authentication public key (key.pub) |
+
+Templates and their versioning metadata both live under =/app/template=,
+so they survive redeploys and are covered by the =backup= relation.
+
+* Enterprise license
+
+Carbone runs fine without a license (Community Edition, forever free).
+Advanced features (dynamic images/colors, barcodes, charts, HTML
+aggregation, PDF operations, ...) require an Enterprise license.
+
+To enable it, drop your =*.carbone-license= file into the config store
+(=/app/config= on the host side, i.e.
+=$SERVICE_CONFIGSTORE/app/config=) and redeploy the service.
+
+* API authentication
+
+Authentication is *disabled by default*: the API is reachable as soon as
+the service is up, which is the expected setup behind the =web-proxy=.
+If you ever need an API key (JWT), enable =CARBONE_AUTHENTICATION=true=,
+generate an EC keypair with =generate-keys=, expose the public key as
+=/app/config/key.pub= and generate a token with =generate-token=.  See
+the upstream "Deploy with Docker" documentation for the exact commands.

carbone/hooks/init

@@ -0,0 +1,47 @@
+#!/bin/bash
+
+## Init is run on host
+## For now it is run every time the script is launched, but
+## it should be launched only once after build.
+
+## Accessible variables are:
+## - SERVICE_NAME        Name of current service
+## - DOCKER_BASE_IMAGE   Base image from which this service might be built if any
+## - SERVICE_DATASTORE           Location on host of the DATASTORE of this service
+## - SERVICE_CONFIGSTORE         Location on host of the CONFIGSTORE of this service
+
+set -e
+
+## The image runs as the unprivileged "carbone" user, while the datastore
+## and configstore bind mounts are created by root.  Both /app/template
+## (templates + metadata.db) and /app/config (config.json, keys, license)
+## must be writable by that user, otherwise the container crash-loops with
+## "EACCES: permission denied, open '/app/config/config.json'".
+uid_gid=($(docker_get_uid_gid "$SERVICE_NAME" "carbone" "carbone")) || exit 1
+uid="${uid_gid[0]}"
+gid="${uid_gid[1]}"
+
+mkdir -p "$SERVICE_DATASTORE/app/template" "$SERVICE_CONFIGSTORE/app/config"
+chown "$uid:$gid" "$SERVICE_DATASTORE/app/template" "$SERVICE_CONFIGSTORE/app/config"
+
+## Carbone starts in stateless mode (document generation only) and binds
+## to 127.0.0.1 by default (see `carbone webserver --help`, v5.15.1).
+## Inside Docker it must:
+##  - listen on all interfaces so the web-proxy can reach it (CARBONE_BIND) ;
+##  - serve the Studio web interface and /carbone-studio.js (CARBONE_STUDIO) ;
+##  - enable stateful template management: stable 64-bit template IDs,
+##    versioning and the GET/POST/PATCH /template endpoints
+##    (CARBONE_TEMPLATE_MANAGEMENT).
+##
+## CARBONE_TEMPLATE_METADATA_FLUSH_CRON defaults to once a day; flushing
+## every 5 minutes shrinks the window where a hard crash (SIGKILL, OOM)
+## would lose template metadata.  The graceful-shutdown flush remains the
+## safety net for redeploys (see docker-compose.stop_grace_period).
+init-config-add "
+$SERVICE_NAME:
+  environment:
+    CARBONE_BIND: \"0.0.0.0\"
+    CARBONE_STUDIO: \"true\"
+    CARBONE_TEMPLATE_MANAGEMENT: \"true\"
+    CARBONE_TEMPLATE_METADATA_FLUSH_CRON: \"*/5 * * * *\"
+"

carbone/metadata.yml

@@ -1,7 +1,20 @@
-## From carbone/carbone-ee:full-5.4.2
+## From carbone/carbone-ee:full-5.15.1
-docker-image: docker.0k.io/carbone-ee:5.4.2
+docker-image: docker.0k.io/carbone-ee:5.15.1
+docker-compose:
+  ## Carbone flushes its template metadata to disk on graceful shutdown.
+  ## Docker's default 10s stop timeout is shorter than Carbone's shutdown
+  ## sequence (exitQuietPeriod + flush), so a plain redeploy would SIGKILL
+  ## it and lose the templates/versioning.  Keep this above Carbone's
+  ## exitDeadline (default 3 min).
+  stop_grace_period: 200s
 data-resources:
+  ## Templates and the template-management metadata store (metadata.db)
+  ## both live here, so they survive redeploys and are covered by backup.
   - /app/template
+config-resources:
+  ## Holds the optional Enterprise license (*.carbone-license) and the
+  ## authentication public key (key.pub).  See README.org.
+  - /app/config
 
 uses:
   web-proxy:

carbone/tests/compose/basic-deploy/compose.yml

@@ -0,0 +1,2 @@
+carbone-test:
+  charm: carbone