feat(tools/forgejo): forge + tracker bridge for Codeberg / Gitea / Forgejo

Add `tools/forgejo/` (or `tools/gitea/` — same API family) as a forge bridge for self-hosted Git forges using the Forgejo / Gitea API. The API is mostly **GitHub-compatible**, so much of `tools/github/` can be ported with minimal changes.

**Suggested capabilities** (mirror the GitHub bridge):

- Issue + PR read/write (same shape as GitHub)
- Repo metadata, labels, milestones
- CI integration — Forgejo Actions is GitHub-Actions-compatible

**Why:** As projects look at GitHub-alternatives, Forgejo/Gitea is the leading self-hostable option. **Codeberg** (codeberg.org) runs Forgejo and hosts a substantial OSS set including KeePassXC client tooling, the F-Droid mirror, and a growing migration set. **Gitea** itself uses Gitea. Some Linux subsystems and Apache podling discussions raise Forgejo as the "exit ramp" if GitHub policies become a problem — having the bridge means a project can move without losing the framework.

**Reference:**

- Forgejo API: https://forgejo.org/docs/latest/admin/api-usage/
- Gitea API: https://docs.gitea.com/api/
- Existing GitHub bridge to port from: [`tools/github/`](../tree/main/tools/github/) — the API similarity means much of the read/write surface ports near-verbatim with endpoint substitution