Pin each MusicMouse host to a deploy branch, and freeze musicmouse

musicmouse_version pointed both hosts at rearchitect-backend, a branch that only
ever existed on a laptop - so the previous commit's rework could never actually
have run. Point each host at a deploy/<host> branch on the remote instead. Those
branches are the deployment record: what is installed on that box right now,
moved with a force-push when you mean to deploy.

musicmouse (Kinderzimmer) is the reason this matters. It is in daily use and
still runs the pre-rearchitecture backend out of /opt/musicmouse_venv and
espmusicmouse/host_driver/main.py. That commit has no python-backend/
pyproject.toml, no python-backend/musicmouse.service and no web/ at all, so this
role cannot install it - and a run would have force-checked-out incompatible
code over a working device first and failed afterwards. Set
mediapi_install_kidsmusic: false there and leave it alone;
deploy/musicmouse records the commit that is installed, for rollback. Add a
stat + fail right after the checkout so the same mistake stops with an
explanation instead of failing three tasks deeper.

Also in the role:

- Install the typing game's curriculum next to config.yml. A config with a
  tippen: section refuses to start without it - curriculum_file is validated as
  must-exist - so musicdolphin's new config needs it present.

- Stop clobbering config.yml. The app writes to it at runtime: parent mode
  patches the volume keys and the remote-control page rewrites the remote:
  block. A plain copy: undid that on every run. Install-once by default, with
  -e pi_musicmouse_force_config=true to push a change deliberately.

- Fill out config-musicdolphin.yml against the current schema: library root and
  cache, an absolute static_dir (../web/dist would resolve to /media/web/dist
  from /media/musicmouse and silently serve nothing), tippen, and the volume
  range for a screen-driven instance. ha: is left commented out until the
  Wohnzimmer-oben entity ids are picked - the ones in the dev config are
  Arbeitszimmer. No mqtt: (it would publish a device of dead entities on a
  simulate-only host) and no lirc:/remote: (this host runs irserver, a serial
  daemon, not the lircd this speaks TCP to).

The curriculum is a verbatim copy of app content, so exclude it from
ansible-lint rather than reformat it away from its source.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

roles/pi_musicmouse/defaults/main.yml

@@ -1,7 +1,9 @@
 ---
 pi_musicmouse_repo: "ssh://git@git.bauer.tech:2222/martin/musicmouse.git"
-# No default on purpose: which tag/branch to run is a per-host decision, set in host_vars.
-# musicmouse_version: "rearchitect-backend"
+# No default on purpose: which branch to run is a per-host decision, set in host_vars.
+# The deploy/<host> branches on the remote are the intended values - move one with
+# `git push -f origin <branch>:deploy/musicdolphin` and re-run this role.
+# musicmouse_version: "deploy/musicdolphin"
 
 pi_musicmouse_python_version: "3.13"
 pi_musicmouse_uv_version: "0.12.10"
@@ -13,3 +15,16 @@ pi_musicmouse_build_cache: "/tmp/musicmouse-build-cache"
 
 # Which files/config-*.yml to install as this host's /media/musicmouse/config.yml.
 pi_musicmouse_config_file: "config-{{ inventory_hostname }}.yml"
+
+# The app owns config.yml at runtime: parent mode writes the volume keys back to it, and
+# the remote-control page rewrites its `remote:` block. So the config is installed once
+# and then left alone, or every ansible run would silently undo those edits. Push a
+# changed config deliberately:
+#
+#   just run mediapis.yml musicdolphin -e pi_musicmouse_force_config=true
+pi_musicmouse_force_config: false
+
+# The typing game's lesson plan, installed next to config.yml. A config with a `tippen:`
+# section will not start without it - curriculum_file is validated as must-exist. Set to
+# "" for a host whose config has no tippen section.
+pi_musicmouse_curriculum_file: "tippen-curriculum.yml"