althing-chamber: add althing-agent-runner as third compose service

Phase 2 daemon added to the althing-chamber stack per forseti's request
(vh/althing@5cd088a..ad1d025). Polls floor_grants WHERE consumed_at IS
NULL AND agents.driver='worldtree', claims via atomic UPDATE, calls
Worldtree's conversation API, posts the response back through the bus
as a broadcast.

Shape matches the existing forseti daemon:
  - Same ${ALTHING_IMAGE} (the binary is already in [project.scripts]
    as of ad1d025)
  - command: ["althing-agent-runner"]
  - Same shared SQLite bind-mount at /app/data
  - No port, no healthcheck (CLI doesn't expose one; same liveness
    story as forseti)

Safe to enable preemptively per forseti — when no driver=worldtree
handles are declared in config, the runner sleeps at
poll_interval_seconds. Multi-instance safe via the atomic claim
primitive (no flock needed).

Compose top comment, README "Services in this stack" table, playbook
header + verify steps all extended to reflect the three-service
shape. Will land on ana-docker on vh/althing's next push (compose
deployed via the elway playbook's upload step; image already carries
the binary).

playbooks/deploy-althing-chamber.yaml

@@ -2,11 +2,12 @@
 # Docker host following the PFI /opt/docker/ convention (ana-docker by
 # default, but the playbook works against any host with Docker in place).
 #
-# Brings up TWO compose services from a single image:
-#   althing-chamber  — FastAPI/HTMX web UI, port 7881 host → 8000 container
-#   althing-forseti  — moderator daemon, no port
+# Brings up THREE compose services from a single image:
+#   althing-chamber       — FastAPI/HTMX web UI, port 7881 host → 8000 container
+#   althing-forseti       — moderator daemon, no port
+#   althing-agent-runner  — Phase 2 worldtree-driver dispatcher, no port
 #
-# Both processes share the SQLite store via the same bind-mount under
+# All three processes share the SQLite store via the same bind-mount under
 # /opt/docker/conf/althing-chamber/data. eventbus.bridge_from_db is the
 # cross-process glue.
 #
@@ -134,3 +135,7 @@ verify:
   - name: forseti container running
     shell: docker ps --filter name=^/althing-forseti$ --format '{{.Status}}' | grep -q '^Up'
     changed_when: "false"
+
+  - name: agent-runner container running
+    shell: docker ps --filter name=^/althing-agent-runner$ --format '{{.Status}}' | grep -q '^Up'
+    changed_when: "false"