BitRouter provider config for opencode. This is a seed,
not yet a registered plugin: it is intentionally absent from plugins.manifest.json,
so the CI matrix, scripts/gen.mjs, and the update workflows do not touch it yet.
opencode.json configures BitRouter as an OpenAI-compatible provider pointing at
BitRouter Cloud. It was moved here out of the openclaw/ package, where it had been
riding along unrelated to that plugin.
Add an entry to plugins.manifest.json (dir opencode, package name, language,
build/test commands, bitrouterCoupling, harness detection) and a generated/
target. just gen and the CI matrix will then pick it up automatically.