Add branding assets and harden .gitignore

Commit Red Bear OS icon and loading background images to the branding recipe source. Update .gitignore to exclude fetched tarballs, build artifacts, and target/ dirs inside local/recipes/ while preserving tracked source code.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

.gitignore

@@ -29,6 +29,12 @@ wget-log
 !local/recipes/**/source/
 !local/recipes/**/source/**
 
+# But not fetched tarballs or build artifacts inside local/
+local/recipes/**/source.tar
+local/recipes/**/source.tar.tmp
+local/recipes/**/target/
+local/recipes/**/build/
+
 # Vendor source trees (fetched, not our code)
 **/amdgpu-source/