feat: Inhibit screensaver during backup operations

Adds logic to prevent the screensaver or screen lock from activating while a backup is in progress.

- Uses a D-Bus call to `org.freedesktop.ScreenSaver.Inhibit` to request a lock.
- The lock is activated when a backup starts.
- The lock is reliably released when the backup finishes, fails, or is cancelled.

core/backup_manager.py

@@ -28,6 +28,59 @@ class BackupManager:
         self.is_system_process = False
         self.app = app
         self.encryption_manager = EncryptionManager(logger, app)
+        self.inhibit_cookie = None
+
+    def _inhibit_screensaver(self):
+        """Prevents the screensaver and auto-suspend during a backup."""
+        if not shutil.which("gdbus"):
+            self.logger.log("gdbus command not found, cannot inhibit screensaver.")
+            return
+
+        try:
+            self.logger.log("Attempting to inhibit screensaver and power management.")
+            command = [
+                "gdbus", "call", "--session", "--dest", "org.freedesktop.ScreenSaver",
+                "--object-path", "/org/freedesktop/ScreenSaver",
+                "--method", "org.freedesktop.ScreenSaver.Inhibit",
+                "Py-Backup", "Backup in progress"
+            ]
+            result = subprocess.run(command, capture_output=True, text=True, check=True)
+            # Output is like "(uint32 12345,)", we need to extract the number.
+            match = re.search(r'uint32\s+(\d+)', result.stdout)
+            if match:
+                self.inhibit_cookie = int(match.group(1))
+                self.logger.log(f"Successfully inhibited screensaver with cookie {self.inhibit_cookie}")
+            else:
+                self.logger.log(f"Could not parse inhibit cookie from gdbus output: {result.stdout}")
+        except FileNotFoundError:
+            self.logger.log("gdbus command not found, cannot inhibit screensaver.")
+        except subprocess.CalledProcessError as e:
+            self.logger.log(f"Failed to inhibit screensaver. D-Bus call failed: {e.stderr}")
+        except Exception as e:
+            self.logger.log(f"An unexpected error occurred while inhibiting screensaver: {e}")
+
+    def _uninhibit_screensaver(self):
+        """Releases the screensaver and auto-suspend lock."""
+        if self.inhibit_cookie is None:
+            return
+        if not shutil.which("gdbus"):
+            self.logger.log("gdbus command not found, cannot uninhibit screensaver.")
+            return
+        
+        try:
+            self.logger.log(f"Attempting to uninhibit screensaver with cookie {self.inhibit_cookie}")
+            command = [
+                "gdbus", "call", "--session", "--dest", "org.freedesktop.ScreenSaver",
+                "--object-path", "/org/freedesktop/ScreenSaver",
+                "--method", "org.freedesktop.ScreenSaver.UnInhibit",
+                str(self.inhibit_cookie)
+            ]
+            subprocess.run(command, capture_output=True, text=True, check=True)
+            self.logger.log("Successfully uninhibited screensaver.")
+        except Exception as e:
+            self.logger.log(f"Failed to uninhibit screensaver: {e}")
+        finally:
+            self.inhibit_cookie = None
 
     def cancel_and_delete_privileged_backup(self, delete_path: str):
         """Cancels a running system backup and deletes the target directory in one atomic pkexec call."""
@@ -169,6 +222,7 @@ rm -f '{info_file_path}'
 
     def start_backup(self, queue, source_path: str, dest_path: str, is_system: bool, is_dry_run: bool = False, exclude_files: Optional[List[Path]] = None, source_size: int = 0, is_compressed: bool = False, is_encrypted: bool = False, mode: str = "incremental", password: Optional[str] = None, key_file: Optional[str] = None):
         self.is_system_process = is_system
+        self._inhibit_screensaver()
         thread = threading.Thread(target=self._run_backup_path, args=(
             queue, source_path, dest_path, is_system, is_dry_run, exclude_files, source_size, is_compressed, is_encrypted, mode, password, key_file))
         thread.daemon = True
@@ -370,6 +424,7 @@ set -e
         finally:
             if is_encrypted and mount_point:
                 self.encryption_manager.cleanup_encrypted_backup(base_dest_path)
+            self._uninhibit_screensaver()
             self.process = None
 
     def _create_info_file(self, pybackup_dir: str, backup_name: str, source_size: int, is_encrypted: bool):