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>

tests/test_foreground_service.py

@@ -0,0 +1,87 @@
+"""Smoke tests for the foreground tracker.
+
+The OS-specific probe code is hard to mock end-to-end inside a CI container,
+so these tests focus on the platform-agnostic surface: the dataclass shape,
+TTL caching, and graceful fallback when the platform probe raises. The
+Windows/Linux/macOS probes themselves are exercised through manual runs.
+"""
+
+from __future__ import annotations
+
+import time
+
+import pytest
+
+from media_server.services import foreground_service as fg
+
+
+def setup_function(_):
+    fg.reset_cache()
+
+
+def test_unavailable_default_shape():
+    info = fg.ForegroundInfo(available=False)
+    d = info.to_dict()
+    assert d["available"] is False
+    assert d["pid"] is None
+    assert d["process_name"] is None
+    assert d["is_fullscreen"] is False
+    assert "platform" in d
+
+
+def test_cache_returns_same_instance(monkeypatch):
+    calls = {"n": 0}
+
+    def fake_probe():
+        calls["n"] += 1
+        return fg.ForegroundInfo(available=True, pid=42, process_name="x.exe")
+
+    monkeypatch.setattr(fg, "_probe", fake_probe)
+
+    a = fg.get_foreground_info()
+    b = fg.get_foreground_info()
+    assert a is b
+    assert calls["n"] == 1
+
+
+def test_cache_force_refresh(monkeypatch):
+    calls = {"n": 0}
+
+    def fake_probe():
+        calls["n"] += 1
+        return fg.ForegroundInfo(available=True, pid=calls["n"])
+
+    monkeypatch.setattr(fg, "_probe", fake_probe)
+
+    fg.get_foreground_info()
+    fg.get_foreground_info(force_refresh=True)
+    assert calls["n"] == 2
+
+
+def test_cache_ttl_expiry(monkeypatch):
+    calls = {"n": 0}
+
+    def fake_probe():
+        calls["n"] += 1
+        return fg.ForegroundInfo(available=True, pid=calls["n"])
+
+    monkeypatch.setattr(fg, "_probe", fake_probe)
+    monkeypatch.setattr(fg, "_CACHE_TTL", 0.0)
+    # Re-bind the cache's TTL by exercising it twice with TTL 0.
+    fg.get_foreground_info()
+    fg.get_foreground_info()
+    assert calls["n"] == 2
+
+
+def test_probe_crash_returns_unavailable(monkeypatch):
+    def boom():
+        raise RuntimeError("kaboom")
+
+    # Force every platform branch to call our crashing probe.
+    monkeypatch.setattr(fg, "_probe_windows", boom)
+    monkeypatch.setattr(fg, "_probe_linux", boom)
+    monkeypatch.setattr(fg, "_probe_macos", boom)
+
+    info = fg._probe()
+    assert info.available is False
+    assert info.error and "kaboom" in info.error