Web UI: fix Plex status text, PLEX_URL/PLEX_TOKEN env, local stem server auto-detect, WEB=0

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

README.md

@@ -30,6 +30,12 @@ The stems folder mirrors the music folder. If a song lives at `Kansas/Leftovertu
   Plex Media Server :32400 ───────────────────────────────▶ library, artwork, playlists
 ```
 
+Three parts, and only stemd is required:
+
+- **stemd** is the daemon. It does the actual separating and nothing else.
+- **Stemify web UI** is optional, for desktop users. stemserve serves it at `/`. It plays the stems streamed from the server, and picks up a local stem server on `localhost:8765` by itself.
+- **iOS and Android apps** are optional and built from this repo too.
+
 - **stemd** works through the library on the GPU, one song at a time, and rescans every 30 minutes for new music.
 - **stemserve** serves the finished stems over HTTP with range requests, waveforms and optional Opus transcodes.
 - **Plex** handles the library, metadata, artwork and playlists.
@@ -132,6 +138,9 @@ To update, copy the new files, rebuild, `docker rm -f` the container and run it
 | `PORT` | `8765` | Listen port |
 | `TOKEN` | empty | If set, requests need `X-Stem-Token` or `?token=` |
 | `INDEX_TTL` | `30` | Seconds between rescans of the stems folder |
+| `PLEX_URL` | empty | Plex address. With `PLEX_TOKEN`, the web UI connects to Plex without signing in |
+| `PLEX_TOKEN` | empty | Plex token. Only handed out to clients that pass `TOKEN`, so set `TOKEN` too |
+| `WEB` | `1` | Set to `0` to turn off the web UI and serve the API only |
 
 </details>