Restructure into backend/ and frontend/ subprojects

- backend/ uses proper Python src layout (src/media_library_viewer_api/)
  with pyproject.toml, hatchling build, and PYTHONPATH=src convention
- frontend/ is a Vite + React + TypeScript SPA
- archive/ preserves the original Streamlit prototype for reference
- Cleaned up root to only contain docs, license, and subproject dirs
- Updated README for the new dual-subproject architecture

backend/src/media_library_viewer_api/routers/dashboard.py

@@ -0,0 +1,69 @@
+"""Dashboard router — media counts, per-library breakdown, now-playing."""
+
+from __future__ import annotations
+
+from typing import Any
+
+from fastapi import APIRouter, Depends
+
+from media_library_viewer_api.dependencies import get_jellyfin_client, get_user_id
+from media_library_viewer_api.clients.jellyfin import JellyfinClient
+
+router = APIRouter(prefix="/api/dashboard", tags=["dashboard"])
+
+
+@router.get("/counts")
+def get_counts(
+    client: JellyfinClient = Depends(get_jellyfin_client),
+    user_id: str = Depends(get_user_id),
+) -> dict[str, int]:
+    """Return total movie/series/episode counts."""
+    return client.media_counts(user_id)
+
+
+@router.get("/libraries")
+def get_library_counts(
+    client: JellyfinClient = Depends(get_jellyfin_client),
+    user_id: str = Depends(get_user_id),
+) -> list[dict[str, Any]]:
+    """Return per-library item counts broken down by type."""
+    libraries = client.libraries(user_id)
+    return client.library_item_counts(user_id, libraries)
+
+
+@router.get("/now-playing")
+def get_now_playing(
+    client: JellyfinClient = Depends(get_jellyfin_client),
+) -> list[dict[str, Any]]:
+    """Return currently active playback sessions with transcode info."""
+    sessions = client.active_sessions()
+    results = []
+    for session in sessions:
+        item = session.get("NowPlayingItem") or {}
+        play_state = session.get("PlayState") or {}
+        transcoding = session.get("TranscodingInfo") or {}
+
+        series = item.get("SeriesName") or ""
+        title = f"{series} - {item.get('Name', '')}" if series else item.get("Name", "Unknown")
+
+        is_transcoding = bool(transcoding)
+        transcode_type = []
+        if is_transcoding:
+            if transcoding.get("IsVideoDirect") is False:
+                transcode_type.append("video")
+            if transcoding.get("IsAudioDirect") is False:
+                transcode_type.append("audio")
+            if not transcode_type:
+                transcode_type.append("active")
+
+        results.append({
+            "user": session.get("UserName") or "Unknown",
+            "title": title,
+            "type": item.get("Type", ""),
+            "state": "paused" if play_state.get("IsPaused") else "playing",
+            "transcoding": "yes" if is_transcoding else "no",
+            "transcoding_type": ", ".join(transcode_type),
+            "device": session.get("DeviceName") or session.get("Client") or "",
+            "session_id": session.get("Id") or "",
+        })
+    return results