docs: add README and LICENSE to Rust client and mux crates

LICENSE

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+MIT License
+
+Copyright (c) 2025 Stephen Waits <steve@waits.net>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# DongLoRa Rust Client
+
+Rust client library for talking to a DongLoRa device — either directly
+over USB or through the [mux daemon](../../mux/).
+
+## What's in Here
+
+- `src/protocol.rs` — wire protocol types (`RadioConfig`, `Command`, `Response`, `ErrorCode`)
+- `src/codec.rs` — COBS framing, frame accumulator
+- `src/discovery.rs` — USB VID:PID device discovery
+- `src/transport.rs` — serial and mux socket transports
+- `src/client.rs` — high-level `Client<T>` with send/recv
+- `src/connect.rs` — auto-detection (mux socket, TCP, direct USB)
+
+## Usage
+
+```rust
+use donglora_client::*;
+
+let mut client = connect_default()?;
+client.ping()?;
+client.set_config(RadioConfig::default())?;
+client.start_rx()?;
+
+loop {
+    if let Some(Response::RxPacket { rssi, snr, payload }) = client.recv()? {
+        println!("RX rssi={rssi} snr={snr} len={}", payload.len());
+    }
+}
+```
+
+## Dependencies
+
+- `cobs` — COBS framing
+- `serialport` — USB serial communication
+- `anyhow` — error handling
+- `tracing` — logging