feat(foreground): track topmost process + browser page title

Adds cross-platform foreground-window tracking and exposes it over REST
(/api/foreground) and the existing WebSocket feed.

- foreground_service.py: Windows probe via ctypes (HANDLE-correct argtypes
  to avoid 64-bit handle truncation); macOS via AppKit; Linux via Xlib
  (Wayland returns unavailable). TTL cache + per-platform fallback.
- browser_url_service.py: when foreground is a recognised browser, extract
  the page title from the window title (browser-name suffix stripped) and
  surface `is_browser` + `browser_page_title`. Optional UIA-based URL
  extraction behind MEDIA_SERVER_BROWSER_UIA env flag (off by default —
  Chromium browsers keep their accessibility tree dormant otherwise).
- websocket_manager: poll foreground every 1s inside the existing status
  loop, broadcast `foreground` on connect and `foreground_update` on
  change. Diff only on user-visible fields to avoid geometry spam.
- WebUI: new editorial card rendered under the monitor list on the
  Display tab — process name, window title, fullscreen/minimized/monitor
  chips, browser block when applicable, exe path, PID, started-ago,
  geometry, platform. 16px inter-section gap matches Settings cadence.
- i18n: 25 new keys added to both en.json and ru.json.

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

media_server/routes/foreground.py

@@ -0,0 +1,26 @@
+"""Foreground (topmost) window/process API."""
+
+import asyncio
+import logging
+
+from fastapi import APIRouter, Depends
+
+from ..auth import verify_token
+from ..services.foreground_service import get_foreground_info
+
+logger = logging.getLogger(__name__)
+
+router = APIRouter(prefix="/api/foreground", tags=["foreground"])
+
+
+@router.get("")
+async def get_foreground(
+    refresh: bool = False, _: str = Depends(verify_token)
+) -> dict:
+    """Return metadata about the foreground window and owning process.
+
+    The probe is cached for ~500ms server-side; pass ``?refresh=1`` to bypass
+    the cache for one-shot queries.
+    """
+    info = await asyncio.to_thread(get_foreground_info, refresh)
+    return info.to_dict()