[FEAT] forgejo_* tools — Forgejo state queries via REST API #9

Add a forgejo_* tool family for Forgejo repos (forgejo.example.com and other Forgejo instances), because the fj CLI has no --json/--format — its output is prose, and agents misread it (a squash-merged PR shows as Closed, costing ~4 wasted round trips to establish merged-vs-abandoned). State queries must hit the Forgejo REST API, not the CLI.

Four tools, mirroring the existing gh_*/gitlab_mr_* families:

• forgejo_issue_list — mirror gh_issue_list (state/label/assignee filters, one line per issue, default state=open limit=20).
• forgejo_issue_view — number, title, state, labels, body truncated ~20 lines, comment count.
• forgejo_issue_close — PATCH /issues/{n} state closed, optional comment via POST /issues/{n}/comments first. Comment is a tool ARGUMENT (never a shell string — avoids backtick command-substitution bug).
• forgejo_pr_status — resolves the merged/closed ambiguity: GET /repos/{owner}/{repo}/pulls/{id} → state/merged/merge_commit_sha/head.sha; if state == closed && merged == false, run git branch -r --contains <head.sha> via runGit to report merged_via: git-squash vs genuinely abandoned.

Full spec (must read): the meta-repo change spec section A. Key design points: new src/lib/forgejo-utils.ts mirrors src/lib/gitlab-utils.ts exactly (getForgejoConfig() from FORGEJO_TOKEN/FORGEJO_HOST or derived from origin remote, getForgejoRepo(cwd), forgejoApi(path, config, init?) → ${host}/api/v1${path} with Authorization: token ${token}); every tool returns a one-line "not configured" string when config is absent; never throw from execute; fixture JSON tests, no live API.

Also update agents/github.md in the consuming config: add the four forgejo_* tool names to the permission list + the rule "Forgejo repos: state queries go through forgejo_*. Never fj … --json/--format. git mutations stay on bash." (If agents/github.md is not in this repo, note that and skip — it lives in the user's opencode config; do not create it here.)