feat(app-binding): lier les presets aux applications

Ajoute la configuration des associations application/preset, le service de suivi du focus, l'intégration GUI et les fichiers d'installation nécessaires.

Ajoute les tests unitaires ciblés des bindings, du service de focus, des migrations et des composants GUI associés.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

DEBIAN/postinst

@@ -14,4 +14,8 @@ if [ -d "/run/systemd/system/" ]; then
   pkill -f input-remapper-service  # might have been started by the gui previously
   systemctl enable input-remapper
   systemctl start input-remapper
+
+  # The focus-service is a per-user service. Enable it globally so it starts in
+  # each user's graphical session (takes effect on next login).
+  systemctl --global enable input-remapper-focus.service 2> /dev/null || true
 fi