Deploy rearchitected MusicMouse backend + web frontend

The app grew a python-backend/ and a web/ frontend, so pi_musicmouse no
longer matches it. Rework the role:

- Install a pinned uv and build the venv with Python 3.13; Raspbian
  Bookworm's python3 is 3.11 and the backend uses PEP 695 syntax.
- pip install python-backend/ instead of a requirements.txt, and take
  the systemd unit straight from the checkout so it can't drift.
- Build web/ on the control machine (no npm on the Pi) and rsync
  web/dist over. Chain the checkout -> install -> build -> sync -> restart
  steps through handlers so a run with no repo change does nothing.
- Per-host config files (config-<host>.yml); the schema now differs
  between a host with a real mouse and a display-only one.
- Version to deploy is per host (musicmouse_version), no default.

Add pi_kiosk: autologin user running startx with Firefox in kiosk mode
and no window manager, for a Pi with a monitor attached. Enabled by
mediapi_has_monitor, defaulting off.

Turn musicdolphin into a display-only instance: serial and audio
simulated, driven entirely through the kiosk page.

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

roles/pi_musicmouse/handlers/main.yml

@@ -0,0 +1,38 @@
+---
+- name: Reinstall musicmouse backend
+  ansible.builtin.command:
+    cmd: "/usr/local/bin/uv pip install --python /opt/musicmouse/.venv/bin/python /opt/musicmouse/python-backend"
+  changed_when: true
+  notify: Restart musicmouse
+
+- name: Build frontend
+  ansible.builtin.command:
+    cmd: npm ci
+    chdir: "{{ pi_musicmouse_build_cache }}/{{ musicmouse_version | regex_replace('/', '_') }}/web"
+  delegate_to: localhost
+  become: false
+  changed_when: true
+  notify: Compile frontend
+
+- name: Compile frontend
+  ansible.builtin.command:
+    cmd: npm run build
+    chdir: "{{ pi_musicmouse_build_cache }}/{{ musicmouse_version | regex_replace('/', '_') }}/web"
+  delegate_to: localhost
+  become: false
+  changed_when: true
+  notify: Sync frontend
+
+- name: Sync frontend
+  ansible.posix.synchronize:
+    src: "{{ pi_musicmouse_build_cache }}/{{ musicmouse_version | regex_replace('/', '_') }}/web/dist/"
+    dest: /opt/musicmouse/web/dist/
+    delete: true
+  notify: Restart musicmouse
+
+- name: Restart musicmouse
+  ansible.builtin.systemd:
+    name: musicmouse
+    state: restarted
+    enabled: "yes"
+    daemon_reload: "yes"