test(e2e): cover host mode, reusable workflows, scheduling, reconnect and CLI flags (#1347)

Extends the e2e suite with scenarios for host labels, local `workflow_call`, label routing, `runner.capacity`, a dropped and restored connection to Gitea, and the daemon's `--once`, `--labels` and `shutdown_timeout` behaviour.

Stacked on https://gitea.com/gitea/runner/pulls/1346, so its commit shows here until that merges. The new scenarios pass locally against gitea/gitea:latest and main-nightly.

Assisted-by: Codet:codet
Co-authored-by: Zettat123 <[email protected]>
Co-authored-by: bircni <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1347
Reviewed-by: Zettat123 <[email protected]>

e2e/reusable_test.go

@@ -0,0 +1,22 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build e2e
+
+package e2e
+
+import "testing"
+
+// testReusableWorkflow runs a local workflow_call workflow and consumes its output.
+func testReusableWorkflow(t *testing.T) {
+	t.Parallel()
+	api, repo := newScenario(t)
+	pushWorkflow(t, api, repo, "reusable_callee.yml")
+	pushWorkflow(t, api, repo, "reusable_caller.yml")
+
+	wfRun := waitForRun(t, api, repo)
+	requireSuccess(t, api, repo, wfRun.ID)
+	if logs := runLogs(t, api, repo, wfRun.ID); commandRow(logs, "e2e-reusable-ran") == "" {
+		t.Errorf("the called workflow did not run:\n%s", logs)
+	}
+}