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>

inputremapper/focus/backends/null.py

@@ -0,0 +1,55 @@
+# -*- coding: utf-8 -*-
+# input-remapper - GUI for device specific keyboard mappings
+# Copyright (C) 2025 sezanzeb <b8x45ygc9@mozmail.com>
+#
+# This file is part of input-remapper.
+#
+# input-remapper is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# input-remapper is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with input-remapper.  If not, see <https://www.gnu.org/licenses/>.
+
+"""A fallback backend used when no focus detection is possible.
+
+This is selected for example on GNOME-Wayland, where the focused window cannot
+be queried without a shell extension. The feature is effectively inactive, but
+the focus-service still runs and reports a clear status.
+"""
+
+from __future__ import annotations
+
+from typing import Optional
+
+from inputremapper.focus.focus_backend import FocusBackend, FocusEvent, OnFocus
+from inputremapper.logging.logger import logger
+
+
+class NullBackend(FocusBackend):
+    """Does nothing. Always available as the last-resort fallback."""
+
+    name = "null"
+
+    @staticmethod
+    def is_available() -> bool:
+        return True
+
+    def start(self, on_focus: OnFocus) -> None:
+        logger.warning(
+            "No supported focus detection is available for this session "
+            "(GNOME-Wayland is not supported). Focus-driven preset binding is "
+            "inactive."
+        )
+
+    def stop(self) -> None:
+        pass
+
+    def get_current(self) -> Optional[FocusEvent]:
+        return None