Add Jellyfin Now Playing + Grafana Panel embed widgets

Two new additive widget kinds:

Jellyfin 'now_playing': like the existing 'activity' widget but filters
to only sessions with active playback (NowPlayingItem present + not
paused). Shows who's actually watching right now. The 'activity' kind
is unchanged (shows all sessions including idle).

Grafana 'panel': embeds a single Grafana panel directly in the app via
an iframe, using Grafana's /d-solo/ endpoint (renders one panel without
dashboard chrome, kiosk=tv). Configurable dashboard_uid, panel_id, and
time range (from/to, defaults now-1h/now). Includes a fallback 'Open in
Grafana' link for when embedding is blocked by X-Frame-Options/CSP. The
'link' kind is unchanged (still builds a deep-link URL).

Backend: new widget configs + definitions on jellyfin/grafana; source
adapter logic (session filter for now_playing; d-solo embed URL for
panel); 6 new tests.

Frontend: JellyfinNowPlayingWidget + GrafanaPanelWidget components;
registry bindings; 6 new tests.

278 backend tests pass (+6); 127 frontend tests pass (+6); lint/build
green both sides.

backend/tests/test_widgets.py

@@ -16,6 +16,7 @@ from media_library_viewer_api.widgets.sources import (
     AlertmanagerWidgetSource,
     BackupsWidgetSource,
     GrafanaWidgetSource,
+    JellyfinWidgetSource,
     ServiceRecord,
     StaticWidgetSource,
 )
@@ -494,3 +495,107 @@ async def test_ssh_task_adapter_records_history_on_run(client):
     runs = store.list_service_task_runs(service_id=service["id"])
     assert len(runs) == 1
     assert runs[0]["status"] == "success"
+
+
+# ---------------------------------------------------------------------------
+# New widget kind tests (jellyfin now_playing + grafana panel)
+# ---------------------------------------------------------------------------
+
+
+def test_jellyfin_definition_has_now_playing_widget():
+    from media_library_viewer_api.integrations.registry import get_service_definition
+
+    definition = get_service_definition("jellyfin")
+    kinds = {wk.kind for wk in definition.widget_kinds}
+    assert "now_playing" in kinds
+    assert "activity" in kinds
+
+
+def test_grafana_definition_has_panel_widget():
+    from media_library_viewer_api.integrations.registry import get_service_definition
+
+    definition = get_service_definition("grafana")
+    kinds = {wk.kind for wk in definition.widget_kinds}
+    assert "panel" in kinds
+    assert "link" in kinds
+
+
+@pytest.mark.asyncio
+async def test_grafana_adapter_builds_panel_embed_url():
+    adapter = GrafanaWidgetSource()
+    service = ServiceRecord(id="s", service_type="grafana", name="g", config={"base_url": "http://g:3000"})
+    result = await adapter.fetch(
+        service,
+        "panel",
+        {"dashboard_uid": "ov", "panel_id": 4, "from_ts": "now-6h", "to_ts": "now"},
+    )
+    assert "embed_url" in result
+    assert result["embed_url"] == ("http://g:3000/d-solo/ov/manage?panelId=4&from=now-6h&to=now&kiosk=tv")
+
+
+@pytest.mark.asyncio
+async def test_grafana_adapter_panel_uses_defaults():
+    adapter = GrafanaWidgetSource()
+    service = ServiceRecord(id="s", service_type="grafana", name="g", config={"base_url": "http://g:3000"})
+    result = await adapter.fetch(service, "panel", {"dashboard_uid": "ov", "panel_id": 2})
+    assert "from=now-1h" in result["embed_url"]
+    assert "to=now" in result["embed_url"]
+
+
+@pytest.mark.asyncio
+async def test_jellyfin_now_playing_filters_active_sessions():
+    """now_playing should exclude idle (no NowPlayingItem) and paused sessions."""
+    adapter = JellyfinWidgetSource()
+    service = ServiceRecord(
+        id="s",
+        service_type="jellyfin",
+        name="jf",
+        config={"base_url": "http://jf:8096"},
+        secrets={"api_key": "k"},
+    )
+    playing_session = {
+        "UserName": "alice",
+        "NowPlayingItem": {"Name": "Movie", "Type": "Movie"},
+        "PlayState": {"IsPaused": False},
+        "DeviceName": "Web",
+    }
+    paused_session = {
+        "UserName": "bob",
+        "NowPlayingItem": {"Name": "Show", "Type": "Episode"},
+        "PlayState": {"IsPaused": True},
+        "DeviceName": "TV",
+    }
+    idle_session = {
+        "UserName": "carol",
+        "PlayState": {"IsPaused": False},
+        "DeviceName": "Phone",
+    }
+    mock_client = SimpleNamespace(sessions=lambda: [playing_session, paused_session, idle_session])
+    with patch("media_library_viewer_api.widgets.sources.JellyfinClient", return_value=mock_client):
+        result = await adapter.fetch(service, "now_playing", {})
+    sessions = result["sessions"]
+    assert len(sessions) == 1
+    assert sessions[0]["user"] == "alice"
+    assert sessions[0]["state"] == "playing"
+
+
+@pytest.mark.asyncio
+async def test_jellyfin_activity_shows_all_sessions():
+    """activity (default) should include idle and paused sessions."""
+    adapter = JellyfinWidgetSource()
+    service = ServiceRecord(
+        id="s",
+        service_type="jellyfin",
+        name="jf",
+        config={"base_url": "http://jf:8096"},
+        secrets={"api_key": "k"},
+    )
+    mock_client = SimpleNamespace(
+        sessions=lambda: [
+            {"UserName": "alice", "NowPlayingItem": {"Name": "M"}, "PlayState": {"IsPaused": False}},
+            {"UserName": "bob", "PlayState": {"IsPaused": False}},
+        ]
+    )
+    with patch("media_library_viewer_api.widgets.sources.JellyfinClient", return_value=mock_client):
+        result = await adapter.fetch(service, "activity", {})
+    assert len(result["sessions"]) == 2