fix(worker): commit as the token's account and check it can push

The worker committed as a hard-coded "gbr-bot", and a token without Write
access only showed up when a build finished and its push failed. On start it
now reads the token's account (GET /user) for the commit author, and
refuses to run if that account can't push to the games repo.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

BUILDER.md

@@ -42,7 +42,7 @@ All through environment variables; nothing about where it runs lives in this rep
 | --- | --- |
 | `PANEL_URL` | The panel the worker takes jobs from |
 | `BUILDER_TOKEN` | Shared secret the panel checks on `/api/v1/builder/**` (same value in the panel's env) |
-| `GITEA_TOKEN` | The bot account's token (repository read/write on this repo): pushes draft branches, opens PRs |
+| `GITEA_TOKEN` | The bot account's token (repository read/write; the account needs Write on this repo): pushes draft branches, opens PRs as that account. Checked when the worker starts |
 | `OLLAMA_URL` | Ollama for the model (or `MODEL_PROVIDER=gemini` with `GEMINI_API_KEY`) |
 | `SEARXNG_URL`, `READER_URL` | A SearXNG instance (JSON API) and a page-to-text reader (`READER_URL/<page url>`) |
 | `MODEL`, `POLL_INTERVAL`, `WORKER_NAME`, `WORK_DIR` | Optional: model name, poll interval (20s), name shown in the panel, work folder |