feat: add NixOS module for HackerGadgets AIO v2 board (uConsole CM5)

- New module: hardware.uconsole-cm5-aio-v2
  - GPIO rail control for GPS (27), LORA (16), SDR (7), USB (23)
  - Systemd oneshot service (aiov2-rails-boot) to apply states at boot
  - aiov2_ctl CLI tool packaged from GitHub source
  - GPS UART support (ttyAMA0, 9600 baud) with dialout group
  - Optional systemd user service for system tray GUI
- Wired into uconsole-cm5 NixOS config + SD image

All rails default OFF — activate on demand with:
  aiov2_ctl <GPS|LORA|SDR|USB> on

hosts/uconsole-cm5/configuration.nix

@@ -26,5 +26,20 @@
   # Firmware
   hardware.enableRedistributableFirmware = true;
 
-  # DSI display fix: le kernel patch est dans flake.nix (patches/0008-panel-cwu50-no-burst.patch)
+  # HackerGadgets AIO v2 board
+  hardware.uconsole-cm5-aio-v2 = {
+    enable = true;
+
+    # Rails actifs au boot
+    bootRails = {
+      GPS  = false;  # activé à la demande via aiov2_ctl GPS on
+      LORA = false;  # activé à la demande via aiov2_ctl LORA on
+      SDR  = false;  # activé à la demande via aiov2_ctl SDR on
+      USB  = false;  # activé à la demande via aiov2_ctl USB on
+    };
+
+    enableGPS = false; # activer quand antenne GPS branchée
+  };
+
+  # DSI display fix: le kernel patch est dans flake.nix (patches/0008-panel-cwu50-fix-init-seq1.patch)
 }