feat: add Arco to Other Software section

[shifty11]

Summary

• Add Arco to the Other Software section
• Arco is a modern GUI-based backup tool based on Borg with encryption, compression, and deduplication

Links

• Forge link: https://github.com/loomi-labs/arco
• pkg.go.dev: https://pkg.go.dev/github.com/loomi-labs/arco
• goreportcard.com: https://goreportcard.com/report/github.com/loomi-labs/arco
• Coverage: N/A (desktop application with GUI, not a library)

Notes

Arco is a desktop application (not a library), similar to other entries in "Other Software" like restic, Duplicacy, hugo, etc.

[github-actions]

Automated Quality Checks (from CONTRIBUTING minimum standards)

• Repo: OK
• pkg.go.dev: OK
• goreportcard: OK (grade unknown)
• coverage: missing

These checks are a best-effort automation and do not replace human review.

[harmonseam-max]