feat(foreground): foreground process sensors + translation key migration

Adds Home Assistant entities for the foreground-process feature shipped
in the media server, plus migrates existing display entities to use HA
translation keys (strings.json / translations/*) so per-language UI text
flows through the standard locale mechanism.

Foreground entities (all share one HA "Foreground" device linked to the
hub via via_device):
- sensor.foreground_process — process name as state + full payload
  (pid, exec path, window title, fullscreen flag, monitor, geometry,
  is_browser, browser_page_title, browser_url, error) as attributes
- sensor.window_title, sensor.pid, sensor.foreground_monitor,
  sensor.process_started (TIMESTAMP device class)
- binary_sensor.fullscreen, binary_sensor.minimized

Data flow:
- ForegroundCoordinator polls GET /api/foreground every 5s (HTTP fallback)
- media_player's WebSocket receiver forwards `foreground` /
  `foreground_update` push frames into the coordinator via
  apply_websocket_snapshot, so sensors update in near-real-time when WS
  is connected and fall back to polling otherwise

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

custom_components/remote_media_player/translations/en.json

@@ -42,6 +42,34 @@
       }
     }
   },
+  "entity": {
+    "binary_sensor": {
+      "primary_display": { "name": "Primary display" },
+      "power_control_supported": { "name": "Power control supported" },
+      "fullscreen": { "name": "Fullscreen" },
+      "minimized": { "name": "Minimized" }
+    },
+    "sensor": {
+      "resolution": { "name": "Resolution" },
+      "foreground_process": { "name": "Foreground process" },
+      "window_title": { "name": "Window title" },
+      "pid": { "name": "PID" },
+      "foreground_monitor": { "name": "Monitor" },
+      "process_started": { "name": "Process started" }
+    },
+    "number": {
+      "brightness": { "name": "Brightness" },
+      "contrast": { "name": "Contrast" }
+    },
+    "switch": {
+      "power": { "name": "Power" }
+    },
+    "select": {
+      "input_source": { "name": "Input source" },
+      "color_preset": { "name": "Color preset" },
+      "picture_mode": { "name": "Picture mode" }
+    }
+  },
   "services": {
     "execute_script": {
       "name": "Execute Script",

custom_components/remote_media_player/translations/ru.json

@@ -42,6 +42,34 @@
       }
     }
   },
+  "entity": {
+    "binary_sensor": {
+      "primary_display": { "name": "Основной дисплей" },
+      "power_control_supported": { "name": "Поддержка управления питанием" },
+      "fullscreen": { "name": "Полноэкранный режим" },
+      "minimized": { "name": "Свёрнуто" }
+    },
+    "sensor": {
+      "resolution": { "name": "Разрешение" },
+      "foreground_process": { "name": "Активный процесс" },
+      "window_title": { "name": "Заголовок окна" },
+      "pid": { "name": "PID" },
+      "foreground_monitor": { "name": "Монитор" },
+      "process_started": { "name": "Запуск процесса" }
+    },
+    "number": {
+      "brightness": { "name": "Яркость" },
+      "contrast": { "name": "Контрастность" }
+    },
+    "switch": {
+      "power": { "name": "Питание" }
+    },
+    "select": {
+      "input_source": { "name": "Источник сигнала" },
+      "color_preset": { "name": "Цветовая температура" },
+      "picture_mode": { "name": "Режим изображения" }
+    }
+  },
   "services": {
     "execute_script": {
       "name": "Выполнить скрипт",