PRE-3: Forge/Gitea adapter (HTTP)

[nextlevelshit]

Part of Epic #1565.

Add Gitea v1 HTTP adapter alongside existing GitHub adapter. Host classifier routes git.librete.ch and other Gitea hosts.

Files:

• New: internal/forge/gitea.go
• Modify: internal/forge/detect.go:14-22 — host classifier
• Modify: internal/forge/client.go:12-24 — adapter dispatch

Acceptance:

• plan-research artifact: Gitea v1 surface mapped (issues, PRs, comments, labels)
• HTTP-based — no tea CLI dependency
• Token auth via env (GITEA_TOKEN)
• Smoke test against git.librete.ch
• Existing GitHub flows untouched

Pipeline: plan-research → impl-issue

[nextlevelshit]

Live smoke validated (see PR #1575)

Build-tagged live test added: internal/forge/gitea_live_test.go (//go:build live, configurable via GITEA_HOST / GITEA_OWNER / GITEA_REPO / GITEA_TOKEN). Run with:

go test -tags live -v -run Live ./internal/forge/...

Verified against codeberg.org/forgejo/forgejo (real Forgejo + Codeberg-hosted):

• ListIssues → 5 issues, labels and IsPR flag correct
• ListPullRequests → 5 PRs, merged-state override confirmed (PR #12325 surfaces as State="merged")

End-to-end happy path on the wire format. CI never runs the live test (missing build tag).