Add Codeberg support

[cyberstorm-nisto]

Summary

Extend didgit.dev to support Codeberg identity attestations.

Implementation

Required

• Codeberg/Gitea OAuth integration
• Codeberg Gist proof mechanism
• Codeberg Events API for contribution tracking
• Codeberg commit verification

Technical Details

• Domain: codeberg.org
• Proof: Public Gist (Gitea-style)
• API: Gitea REST API v1

Codeberg runs Gitea, so this adapter can be reused for any Gitea instance.

See EXTENDING.md for implementation guide.

Acceptance Criteria

• User can bind codeberg.org:username to wallet
• User can create proof gist via Codeberg OAuth
• Contributions from Codeberg repos can be attested
• Generic Gitea adapter for self-hosted instances