config: one resolver for which remote this board rides

github.remote() decided it for PRs; sync assumed 'origin'. The answer
moves to config, which already owns BOARD_GIT_REMOTE, resolved on demand
so config still shells out nothing at import. github.remote() becomes a
thin call to it, and git_remotes() lets a caller check whether the name
resolves to a remote that exists rather than falling back silently.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

manager/core/github.py

@@ -39,11 +39,9 @@ def _run(cmd: list[str], cwd: Path | None = None, timeout: int = 60) -> subproce
 
 
 def remote() -> str | None:
-    if config.GIT_REMOTE:
-        return config.GIT_REMOTE
-    result = _run(["git", "remote"])
-    names = result.stdout.split()
-    return names[0] if names else None
+    """Where this board's work goes. Resolved in config, which sync asks
+    too — the two halves of team mode must never name different remotes."""
+    return config.git_remote()
 
 
 def gh_available() -> bool: