refactor: rename project to DongLoRa

Rebrand from lora-dongle to DongLoRa (portmanteau of dongle + LoRa).
Lowercase donglora in Cargo package name, firmware filenames, and code.
Splash screen shows "DongLoRa" in 9x15 bold.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -1,4 +1,4 @@
-# lora-dongle
+# DongLoRa
 
 Transparent LoRa radio over USB. Plug in a board, talk LoRa from your host.