fix: remove stale postcard/serde references from README, DESIGN.md, CHANGELOG, donglora.py

CHANGELOG.md

@@ -10,7 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/).
 ### Added
 
 - Transparent LoRa radio over USB CDC-ACM (VID `1209`, PID `5741`)
-- COBS-framed postcard binary protocol (8 commands, 6 responses)
+- COBS-framed fixed-size LE binary protocol (8 commands, 6 responses)
 - Radio configuration: frequency, bandwidth, spreading factor, coding rate, TX power
 - Continuous RX mode with RSSI/SNR per packet
 - Single-shot TX with optional per-packet config override

DESIGN.md

@@ -97,8 +97,8 @@ keep, but never prematurely.
 
 | Decision | Choice | Why |
 |---|---|---|
-| USB framing | COBS + postcard | Compact, `no_std` native, battle-tested |
-| Serialization | postcard + serde | Zero-alloc binary codec, perfect for embedded |
+| USB framing | COBS | Compact, `no_std`, zero-overhead frame delimiting |
+| Serialization | Fixed-size LE | Every field at a known offset. No varints, no surprises |
 | Async runtime | Embassy | De facto standard for async embedded Rust |
 | Display | Radio status dashboard | Freq, BW, SF, packet counts, RSSI/SNR |
 | Boot behavior | Idle until host commands | Host-driven principle |

README.md

@@ -23,10 +23,9 @@ and gets out of the way. No mesh logic, no protocol opinions, no config files.
 
 ## Protocol
 
-DongLoRa speaks a binary protocol over USB CDC-ACM: COBS-framed
-[postcard](https://postcard.jamesmunns.com/) messages. 8 commands,
-6 response types — everything you need to configure the radio,
-transmit, and receive.
+DongLoRa speaks a binary protocol over USB CDC-ACM: COBS-framed,
+fixed-size little-endian messages. 8 commands, 6 response types —
+everything you need to configure the radio, transmit, and receive.
 
 See **[docs/PROTOCOL.md](docs/PROTOCOL.md)** for the complete wire format
 specification with worked examples.

examples/donglora.py

@@ -1,7 +1,7 @@
 """DongLoRa host library — connect, configure, send/receive LoRa packets.
 
 This is a minimal helper for the example scripts. It implements the
-DongLoRa USB protocol (COBS-framed postcard) just enough to be useful.
+DongLoRa USB protocol (COBS-framed fixed-size LE) just enough to be useful.
 See docs/PROTOCOL.md for the full specification.
 """
 # /// script