Keep the media-pi roles working on trixie

- pi_hifiberry_amp: the boot config lives at /boot/firmware/config.txt.
- pi_sysdweb: install python3-dbus and python3-systemd from apt, which trixie ships at
  the versions sysdweb needs; bookworm gets the headers pip needs to build dbus-python
  1.4 itself.
- pi_squeezeserver: trixie images have no iptables, and so cannot have the port 80
  redirect that absent.yml removes - skip that step there instead of failing.
- pi_modern_shell_env, pi_slint_frontend: read facts through `ansible_facts` rather than
  the deprecated injected `ansible_*` variables.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

roles/pi_hifiberry_amp/tasks/main.yml

@@ -1,7 +1,7 @@
 ---
 - name: Deactivate normal audio
   ansible.builtin.lineinfile:
-    path: /boot/config.txt
+    path: /boot/firmware/config.txt
     regexp: "^#?dtparam=audio=on"
     line: "#dtparam=audio=on"
   notify: Reboot after HiFiBerry boot config change