feat(const,strings,readme): adb_command consts/service name, options toggle strings, curated DEFAULT_APP_DIRECTORY and README service notes (completes P4-2 unit 1)

custom_components/nvidia_shield/strings.json

@@ -78,7 +78,8 @@
           "adb_store_app_info": "Show App Media Info",
           "adb_host": "ADB Host",
           "adb_port": "ADB Port",
-          "app_name_map": "Apps name/icon map"
+          "app_name_map": "Apps name/icon map",
+          "adb_command_enabled": "Enable raw ADB shell service"
         },
         "data_description": {
           "jellyfin_entity": "The Jellyfin media_player for this device. Session stream info is read from the HA Jellyfin integration's existing coordinator \u2014 no extra config needed.",
@@ -89,7 +90,8 @@
           "adb_store_app_info": "Show title and artist from non-Jellyfin apps. Disable for privacy.",
           "adb_host": "IP address for ADB connection. Leave blank to auto-detect from the Android TV Remote integration.",
           "adb_port": "ADB port (default 5555).",
-          "app_name_map": "One entry per line, package=name (e.g. ar.tvplayer.tv=TiviMate). The friendly name resolves after the Android TV Remote entity and the protocol push; icons follow the media image lookup by name. Leave blank to clear."
+          "app_name_map": "One entry per line, package=name (e.g. ar.tvplayer.tv=TiviMate). The friendly name resolves after the Android TV Remote entity and the protocol push; icons follow the media image lookup by name. Leave blank to clear.",
+          "adb_command_enabled": "Adds the nvidia_shield.adb_command service (raw ADB shell over the persistent connection). Security-relevant: leave off unless you need it \u2014 it is the same opt-in posture as the core androidtv integration."
         }
       }
     }