feat(#493): api-key backend support (useApiKey + backendEnvironmentFile)

hive-agent/src/main.rs

@@ -559,6 +559,10 @@ async fn serve_main<S: Surface>(socket: &Path, poll_ms: u64) -> Result<()> {
     let claude_dir = login::default_dir();
     let initial = LoginState::from_dir(&claude_dir);
     tracing::info!(state = ?initial, claude_dir = %claude_dir.display(), "harness boot");
+    // Config fact, stamped once — see `harness_state::write_api_key_mode`'s
+    // doc for why hive-c0re needs this to stop reporting `needs_login` for
+    // an agent whose `~/.claude/` is empty by design.
+    harness_state::write_api_key_mode(login::using_api_key());
     let login_state = Arc::new(Mutex::new(initial));
     let bus = Bus::new();
     // Set by the web UI's `/api/cancel` on a successful SIGINT, read-and-