feat(led-tool): browser settings editor with Web Serial

Add static editor, host_ports filtering, Flask /editor and REST APIs
for ports and led-cli read/write; document standalone and embedded use.

Co-authored-by: Cursor <cursoragent@cursor.com>

README.md

@@ -36,6 +36,25 @@ Connection is always via **`-p` / `--port`** (default `/dev/ttyACM0`). There is
 
 Run **`python cli.py -h`** for the full epilog and argument list.
 
+## Web UI (`static/` + `web.py`)
+
+Edit **`settings.json`** in the browser:
+
+- **Web Serial** — USB on the machine running the browser (Chrome/Edge). Use **Connect USB**, then **Download** / **Upload**.
+- **Host serial** — USB on the Pi/PC running **`led-cli`** (port list + **`led-cli`** merge/upload).
+
+**Standalone (Flask):**
+
+```bash
+cd led-tool
+python web.py
+# open http://<host>:5000/editor
+```
+
+**Embedded in led-controller:** open **LED Tool** in the main UI, or visit **`/led-tool/editor`**.
+
+Legacy Flask form UI remains at **`/`** on port 5000; prefer **`/editor`** for Web Serial support.
+
 ## License
 
 See **LICENSE** in this directory.