fix(display-manager): lazy launch by default + minimize unassigned apps

- autolaunch default: True → False (on-demand only, saves GPU on startup)
- add ProcessManager.minimize() to minimize a window to taskbar
- add win32_utils.minimize_window() (SW_MINIMIZE via user32)
- DisplayManager._minimize_unassigned(): after each app switch, minimize
  every running app not currently assigned to any screen, freeing iGPU
  resources (critical on J6412 UHD 600 with limited EUs)

Background: J6412 Intel UHD 600 has only 16 EUs @ 800 MHz. Running
AR-ECDIS (MapLibre GL) and GPS (OpenLayers) simultaneously consumes ~60%
iGPU. By minimizing inactive apps Windows suspends their GPU presentation
chain, dropping idle GPU load near zero.

AR_electronics — AR-Autopilot Project

display_manager/config.py

@@ -38,7 +38,7 @@ class DisplayManagerConfig:
     apps: dict[str, AppExeConfig] = field(default_factory=dict)
     button_position: str = "top-right"   # top-right | top-left | bottom-right | bottom-left
     button_margin: int = 12              # px from screen edge
-    autolaunch: bool = True              # launch apps on startup if exe exists
+    autolaunch: bool = False             # launch all apps on startup (False = on-demand only)
 
     # ------------------------------------------------------------------ I/O
     @classmethod