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/README.md

@@ -2,6 +2,38 @@
 
 FastAPI backend serving the REST API for Jellyfin media browsing, SSH file inspection, and server monitoring.
 
+## Project structure
+
+```
+backend/
+├── pyproject.toml
+├── README.md
+├── src/
+│   └── media_library_viewer_api/
+│       ├── __init__.py
+│       ├── main.py              # FastAPI app entrypoint
+│       ├── config.py            # pydantic-settings config
+│       ├── dependencies.py      # Dependency injection
+│       ├── path_utils.py        # Jellyfin→SSH path resolution
+│       ├── jobs.py              # Job templates
+│       ├── utils.py             # Formatting helpers
+│       ├── routers/
+│       │   ├── dashboard.py
+│       │   ├── monitoring.py
+│       │   ├── media.py
+│       │   ├── files.py
+│       │   └── jobs.py
+│       ├── clients/
+│       │   ├── jellyfin.py
+│       │   ├── resources.py
+│       │   └── ssh.py
+│       ├── domain/
+│       │   └── media.py
+│       └── services/
+│           └── media_index.py
+└── tests/
+```
+
 ## Setup
 
 ```bash
@@ -11,12 +43,6 @@ source .venv/bin/activate
 pip install -e '.[dev]'
 ```
 
-Or install dependencies directly:
-
-```bash
-pip install fastapi uvicorn[standard] pydantic-settings paramiko requests python-dotenv pandas
-```
-
 ## Configuration
 
 Create a `.env` file in the project root (or set environment variables):
@@ -40,7 +66,13 @@ REMOTE_PATH_PREFIX=
 
 ```bash
 cd backend
-uvicorn main:app --reload --port 8000
+uvicorn media_library_viewer_api.main:app --reload --port 8000
+```
+
+Or with PYTHONPATH if not installed:
+
+```bash
+PYTHONPATH=src uvicorn media_library_viewer_api.main:app --reload --port 8000
 ```
 
 API docs available at: http://localhost:8000/docs
@@ -51,9 +83,10 @@ API docs available at: http://localhost:8000/docs
 - `GET /api/dashboard/libraries` — Per-library breakdown
 - `GET /api/dashboard/now-playing` — Active playback sessions
 - `GET /api/monitoring/status` — Collector status
-- `GET /api/monitoring/metrics` — Resource samples
+- `GET /api/monitoring/metrics` — Resource samples (last hour)
 - `GET /api/monitoring/disk` — Disk space
 - `POST /api/monitoring/start|stop|restart` — Collector controls
+- `GET /api/monitoring/diagnostics` — Collector debug info
 - `GET /api/media/status` — Index status
 - `POST /api/media/build` — Rebuild index
 - `GET /api/media/query` — Query with filters/sort/pagination