feat(update): felis update 读取维护窗口并报告当前是否在窗口内，窗口外应用前警告，面板与文档写明窗口为提示性

cmd/felis/update_window_test.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"errors"
+	"testing"
+	"time"
+
+	"felis.lolicon.best/internal/updates"
+)
+
+func TestRenderWindowLinePlacesNowAgainstTheWindow(t *testing.T) {
+	prev := time.Local
+	time.Local = time.FixedZone("CST", 8*3600)
+	t.Cleanup(func() { time.Local = prev })
+
+	w := updates.Window{
+		Start: time.Date(2026, 9, 26, 18, 0, 0, 0, time.UTC),
+		End:   time.Date(2026, 9, 26, 20, 0, 0, 0, time.UTC),
+	}
+	cases := []struct {
+		name string
+		w    updates.Window
+		err  error
+		now  time.Time
+		want string
+	}{
+		{"unreadable", updates.Window{}, errors.New("connection refused"), w.Start, "Maintenance window: unknown (connection refused).\n"},
+		{"unset", updates.Window{}, nil, w.Start, "Maintenance window: not set; apply whenever suits you.\n"},
+		{"half set", updates.Window{Start: w.Start}, nil, w.Start, "Maintenance window: not set; apply whenever suits you.\n"},
+		{"at the opening instant", w, nil, w.Start, "Maintenance window: open now, until 2026-09-27 04:00 CST.\n"},
+		{"before", w, nil, w.Start.Add(-time.Minute), "Maintenance window: opens 2026-09-27 02:00 CST, until 2026-09-27 04:00 CST. Felis applies nothing on its own; run the apply commands inside it.\n"},
+		{"at the closing instant", w, nil, w.End, "Maintenance window: ended 2026-09-27 04:00 CST; set a new one in the panel before applying.\n"},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := renderWindowLine(tc.w, tc.err, tc.now); got != tc.want {
+				t.Fatalf("got  %q\nwant %q", got, tc.want)
+			}
+		})
+	}
+}