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_registry.py

@@ -0,0 +1,45 @@
+"""Static metadata for the four AR Bridge applications."""
+from __future__ import annotations
+from dataclasses import dataclass
+
+@dataclass(frozen=True)
+class AppMeta:
+    id: str
+    name: str
+    icon: str          # emoji used in the button popup
+    color: str         # hex accent colour for the card
+    description: str
+
+# Ordered list — shown in this order in the popup
+APPS: list[AppMeta] = [
+    AppMeta(
+        id="autopilot",
+        name="AR-Autopilot",
+        icon="⛵",
+        color="#2563EB",
+        description="Autopilot control display",
+    ),
+    AppMeta(
+        id="ecdis",
+        name="AR-ECDIS",
+        icon="🗺",
+        color="#22C55E",
+        description="Electronic chart display",
+    ),
+    AppMeta(
+        id="compass",
+        name="Compass",
+        icon="🧭",
+        color="#F59E0B",
+        description="Ship motion & compass",
+    ),
+    AppMeta(
+        id="gps",
+        name="GPS Navigator",
+        icon="📍",
+        color="#8B5CF6",
+        description="GPS navigation display",
+    ),
+]
+
+APP_BY_ID: dict[str, AppMeta] = {a.id: a for a in APPS}