chore: housekeeping for v0.3 prep

- Pin KUBESOLO_VERSION in versions.env (was soft-defaulted in fetch-components.sh)
- Gitignore screenshots, macOS resource forks, and common image extensions
- Update README roadmap: x86_64 stable, ARM64 generic in progress (v0.3),
  ARM64 RPi paused pending hardware
- Add docs/ci-runners.md documenting the Odroid arm64-linux Gitea runner

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -18,8 +18,19 @@ build/rootfs-work/
 
 # OS
 .DS_Store
+._*
 Thumbs.db
 
+# Photos / screenshots — keep documentation images under docs/ instead
+*.PNG
+*.png
+*.JPG
+*.jpg
+*.JPEG
+*.jpeg
+*.HEIC
+*.heic
+
 # Go
 update/update-agent
 cloud-init/cloud-init-parser