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/__init__.py

@@ -25,6 +25,7 @@ from .const import (
     SERVICE_PLAY_MEDIA_FILE,
 )
 from .display_coordinator import DisplayCoordinator
+from .foreground_coordinator import ForegroundCoordinator
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -88,11 +89,20 @@ async def async_setup_entry(hass: HomeAssistant, entry: ConfigEntry) -> bool:
     except Exception as err:  # noqa: BLE001 - first refresh wraps its own errors
         _LOGGER.warning("Initial display monitor fetch failed, will retry: %s", err)
 
+    # Foreground coordinator — shared by sensor + binary_sensor platforms and
+    # nudged by the media-player WebSocket receiver when it gets a push.
+    foreground_coordinator = ForegroundCoordinator(hass, client)
+    try:
+        await foreground_coordinator.async_config_entry_first_refresh()
+    except Exception as err:  # noqa: BLE001
+        _LOGGER.warning("Initial foreground fetch failed, will retry: %s", err)
+
     # Store client in hass.data
     hass.data.setdefault(DOMAIN, {})
     hass.data[DOMAIN][entry.entry_id] = {
         "client": client,
         "display_coordinator": display_coordinator,
+        "foreground_coordinator": foreground_coordinator,
     }
 
     # Register services if not already registered