chore: drop unused doc/publish.sh — radicle-ci-broker

This was a remenant from an older era of Radicle CI.

build(Makefile): build subplot as HTML

tests(ci-broker.md): add scenario for empty queue

test(ci-broker.md): change shutdown scenario to verify cleanliness

 set -eu
 cat > /dev/null
 echo '{"response":"triggered","run_id":{"id":"xyzzy"}}'
 # Simulate a CI run that takes a while.
 sleep 2
 echo '{"response":"finished","result":"success"}'
 (
 echo "This is an adapter error: Mordor"

 ~~~
 ## Shuts down when requested
 ## Can shut down cleanly
 _Want:_ The test suite can request the CI broker to shut down
 cleanly, and it doesn't result in an error.
 _Want:_ The node operator can instrut the running CI broker to shut down after
 currently executing runs finish.
 _Why:_ In the integration test suite, we need to start and
 stop the CI broker many times. We need to easily detect errors.
 _Why:_This is useful for both the CI broker test suite and for operators to
 shut down service for maintenance.
 _Who:_ `cib-devs`
 _Who:_ `cib-devs`, `node-ops`
 We use a special magic fake node event to signal shutdown: a
 `RefsFetched` event with a skipped update for a ref "`shutdown`" and
 an object id of all zeros. This should be sufficiently impossible to
 happen in real life.
 We verify this by starting a relatively long-running CI run and also telling
 `cib` to shut down, and then verifying the CI run finished successfully.
 ~~~scenario
 given a Radicle node, with CI configured with broker.yaml and adapter dummy.sh
 given a Git repository xyzzy in the Radicle node
 given the Radicle node emits a refsUpdated event for xyzzy
 when I run ./env.sh synthetic-events synt.sock event.json --log log.txt
 when I try to run ./env.sh cib --config broker.yaml insert
 when I run cibtool --db ci-broker.db trigger --repo xyzzy --commit HEAD
 when I run cibtool --db ci-broker.db event shutdown
 when I try to run ./env.sh cib --config broker.yaml queued
 then command is successful
 when I run cibtool --db ci-broker.db run list
 then stdout is empty
 when I run cibtool --db ci-broker.db run list --json
 then stdout contains "success"
 ~~~

 all: architecture.html userguide.html overview.html
 publish: all
 	bash publish.sh
 architecture.html: architecture.subplot architecture.md Makefile messages.md
 messages.md: messages.sh messages.txt

 #!/bin/bash
 set -xeuo pipefail
 if [ "${RADICLE_CI_BROKER_WEBROOT:-unset}" != unset ]; then
 	echo web root set, publishing arch doc there
 	install -d -m 0755 "$RADICLE_CI_BROKER_WEBROOT"
 	install -m 0644 ./*.html "$RADICLE_CI_BROKER_WEBROOT"
 else
 	echo web root is not set, not publishing arch doc
 fi