refactor: migrate from Codeberg to Gitea and rename rhemawave to radiantwave

- Update all Codeberg URLs to gitea.radiantwavetech.com/RadiantWaveTech/
- Rename flake inputs: rhemawave → radiantwave, rhemawave-dev → radiantwave-dev
- Rename NixOS configs: rhemawavekiosk* → radiantwavekiosk*
- Update systemd services, data paths, and binary references
- Rename plymouth theme files
- Update CI workflow, documentation, and build scripts

plymouth-theme/radiantwave.plymouth

@@ -0,0 +1,8 @@
+[Plymouth Theme]
+Name=RadiantWave
+Description=RadiantWave kiosk splash screen
+ModuleName=script
+
+[script]
+ImageDir=/usr/share/plymouth/themes/radiantwave
+ScriptFile=/usr/share/plymouth/themes/radiantwave/radiantwave.script

plymouth-theme/rhemawave.plymouth

@@ -1,8 +0,0 @@
-[Plymouth Theme]
-Name=RhemaWave
-Description=RhemaWave kiosk splash screen
-ModuleName=script
-
-[script]
-ImageDir=/usr/share/plymouth/themes/rhemawave
-ScriptFile=/usr/share/plymouth/themes/rhemawave/rhemawave.script