Add 'good first issue' and 'help wanted' labels across all repos

[zeevdr]

Description

Tag appropriate issues with good first issue and help wanted labels to attract external contributors. GitHub surfaces these labels specially in the contributor discovery UI.

Acceptance criteria

• Ensure good first issue and help wanted labels exist in all repos
• Review open issues and tag any that are suitable for newcomers
• Add guidance in CONTRIBUTING.md about how to find starter issues

Notes

• good first issue should be truly easy — clear scope, no deep context needed
• help wanted can be harder but should be well-documented
• GitHub's "Explore" page surfaces repos with these labels to potential contributors