feat: AR Display Manager — multi-monitor floating app switcher

Adds the AR Display Manager daemon (Task #9):

- display_manager/ package with 8 modules:
  - app_registry.py   : static metadata for the 4 bridge apps
  - config.py         : JSON-persisted config + per-screen layout store
  - win32_utils.py    : ctypes wrappers (EnumWindows, SetWindowPos, ShowWindow)
  - process_manager.py: launch + track app processes, HWND lookup
  - floating_button.py: always-on-top 52×52 px AR button per monitor
                        with draggable placement + custom-painted popup
  - display_manager.py: orchestrator (QScreens → buttons → app placement
                        + system tray with Settings/Launch/Quit)
  - settings_dialog.py: modal dialog for exe paths, button position,
                        and Windows autostart toggle
  - autostart.py      : HKCU Run registry read/write helpers
- display_manager_main.py at repo root: launcher script
- Studio Overview tab: "Lanzar Display Manager" button
- pyproject.toml: display-manager optional dependency group (PySide6)

Layout persistence: ~/.ar-autopilot/display_manager/layout.json
Config:            ~/.ar-autopilot/display_manager/config.json
Supports up to 4 monitors (2 HDMI native + 2 USB DisplayLink).
Double-click tray icon to toggle button visibility.

AR_electronics — AR-Autopilot Project

display_manager/app.py

@@ -0,0 +1,45 @@
+"""AR Display Manager entry point."""
+from __future__ import annotations
+
+import signal
+import sys
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+
+
+def run(argv: list[str] | None = None) -> int:
+    """Launch the AR Display Manager daemon."""
+    try:
+        from PySide6.QtWidgets import QApplication
+    except ImportError:
+        sys.stderr.write(
+            "PySide6 is not installed. Run:\n\n"
+            "    pip install PySide6\n"
+        )
+        return 2
+
+    signal.signal(signal.SIGINT, signal.SIG_DFL)  # Ctrl+C kills the process
+
+    app = QApplication(argv if argv is not None else sys.argv)
+    app.setApplicationName("AR Display Manager")
+    app.setQuitOnLastWindowClosed(False)   # keep running when popup closes
+
+    # Brand icon
+    from PySide6.QtGui import QIcon
+    _logo = REPO_ROOT / "display" / "assets" / "images" / "ar_logo_full.png"
+    if _logo.exists():
+        app.setWindowIcon(QIcon(str(_logo)))
+
+    # Apply brand stylesheet
+    from arautopilot.studio.ar_style import apply_ar_style
+    apply_ar_style(app)
+
+    from display_manager.display_manager import DisplayManager
+    _mgr = DisplayManager(app)  # noqa: F841 — kept alive via QObject parent=None
+
+    return app.exec()
+
+
+if __name__ == "__main__":
+    sys.exit(run())