T1.4: Create src/scheduler; move scheduler logic

Move scheduler.go and scheduler_test.go from src/core to the new
src/scheduler package. The scheduler still takes *[]domain.Job and
*core.Store (storage moves in T1.5). Update src/gui/app.go to import
the new package; rename the local variable to sched to avoid shadowing
the scheduler package name.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/scheduler/scheduler_test.go

@@ -0,0 +1,110 @@
+package scheduler
+
+import (
+	"strings"
+	"testing"
+	"time"
+
+	"gitea.mixdep.ru/mix/gosentry/src/domain"
+)
+
+func TestNextRunTimeRejectsInvalidSchedules(t *testing.T) {
+	from := time.Date(2026, 6, 14, 12, 0, 0, 0, time.UTC)
+	cases := []struct {
+		schedule string
+		desc     string
+	}{
+		{"", "empty string"},
+		{"   ", "whitespace only"},
+		{"@every", "bare @every without duration"},
+		{"@every xyz", "invalid @every duration string"},
+		{"@every -1s", "negative @every duration"},
+		{"@every 0s", "zero @every duration"},
+		{"not-a-cron", "invalid cron expression"},
+		{"60 * * * *", "cron minute out of range"},
+	}
+	for _, tc := range cases {
+		_, ok := nextRunTime(tc.schedule, from)
+		if ok {
+			t.Errorf("nextRunTime(%q) [%s]: expected false, got true", tc.schedule, tc.desc)
+		}
+	}
+}
+
+func TestPrepareNextRunSetsDisplayString(t *testing.T) {
+	jobs := []domain.Job{{Schedule: "*/5 * * * *", Enabled: true}}
+	s := &Scheduler{jobs: &jobs}
+	from := time.Date(2026, 6, 14, 12, 3, 0, 0, time.UTC)
+
+	s.prepareNextRun(&jobs[0], from)
+
+	want := "2026-06-14 12:05:00"
+	if jobs[0].NextRun != want {
+		t.Errorf("NextRun: got %q, want %q", jobs[0].NextRun, want)
+	}
+	wantDue := time.Date(2026, 6, 14, 12, 5, 0, 0, time.UTC)
+	if !jobs[0].NextDue.Equal(wantDue) {
+		t.Errorf("NextDue: got %v, want %v", jobs[0].NextDue, wantDue)
+	}
+}
+
+func TestPrepareNextRunSetsInvalidScheduleLabel(t *testing.T) {
+	jobs := []domain.Job{{Schedule: "not-a-cron", Enabled: true}}
+	s := &Scheduler{jobs: &jobs}
+
+	s.prepareNextRun(&jobs[0], time.Now())
+
+	if jobs[0].NextRun != "Invalid schedule" {
+		t.Errorf("NextRun: got %q, want 'Invalid schedule'", jobs[0].NextRun)
+	}
+	if !jobs[0].NextDue.IsZero() {
+		t.Errorf("NextDue should be zero for invalid schedule, got %v", jobs[0].NextDue)
+	}
+}
+
+func TestNextRunTimeSupportsEvery(t *testing.T) {
+	from := time.Date(2026, 6, 14, 12, 0, 0, 0, time.UTC)
+	next, ok := nextRunTime("@every 10s", from)
+	if !ok {
+		t.Fatal("expected @every schedule to parse")
+	}
+	if want := from.Add(10 * time.Second); !next.Equal(want) {
+		t.Fatalf("expected %s, got %s", want, next)
+	}
+}
+
+func TestNextRunTimeSupportsCron(t *testing.T) {
+	from := time.Date(2026, 6, 14, 12, 3, 0, 0, time.UTC)
+	next, ok := nextRunTime("*/5 * * * *", from)
+	if !ok {
+		t.Fatal("expected cron schedule to parse")
+	}
+	want := time.Date(2026, 6, 14, 12, 5, 0, 0, time.UTC)
+	if !next.Equal(want) {
+		t.Fatalf("expected %s, got %s", want, next)
+	}
+}
+
+func TestRunningOutputIncludesInvocation(t *testing.T) {
+	started := time.Date(2026, 6, 17, 23, 40, 0, 0, time.Local)
+	job := domain.Job{
+		Name:             "Backup",
+		Command:          `C:\Program Files\FreeFileSync\FreeFileSync.exe`,
+		Arguments:        `D:\Local\Jobs\Auto.ffs_batch`,
+		SuccessExitCodes: "0,1",
+	}
+
+	output := runningOutput(job, "Manual", started)
+	for _, want := range []string{
+		"Running since 2026-06-17 23:40:00",
+		"Manual",
+		job.Command,
+		job.Arguments,
+		"0,1",
+		"start_only",
+	} {
+		if !strings.Contains(output, want) {
+			t.Fatalf("expected running output to contain %q, got:\n%s", want, output)
+		}
+	}
+}