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>

Cargo.toml

@@ -1,5 +1,5 @@
 [package]
-name = "lora-dongle"
+name = "donglora"
 version = "0.1.0"
 edition = "2021"
 build = "build.rs"