feat(infra): add scheduler and worker-generate standalone processes

Extract monitoring recovery/inspection workers and schedule dispatch
into a dedicated scheduler process. Add worker-generate process for
article generation and template-assist queue consumption. Introduce
shared/schedule runtime for cron-based worker lifecycle management.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/internal/shared/schedule/runtime.go

@@ -0,0 +1,68 @@
+package schedule
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	cron "github.com/robfig/cron/v3"
+)
+
+var cronParser = cron.NewParser(
+	cron.SecondOptional |
+		cron.Minute |
+		cron.Hour |
+		cron.Dom |
+		cron.Month |
+		cron.Dow |
+		cron.Descriptor,
+)
+
+func Parse(cronExpr string) (cron.Schedule, error) {
+	trimmed := strings.TrimSpace(cronExpr)
+	if trimmed == "" {
+		return nil, fmt.Errorf("cron expression is required")
+	}
+
+	schedule, err := cronParser.Parse(trimmed)
+	if err != nil {
+		return nil, fmt.Errorf("parse cron expression %q: %w", trimmed, err)
+	}
+	return schedule, nil
+}
+
+func ComputeNextRun(cronExpr string, startAt, endAt *time.Time, now time.Time) (*time.Time, error) {
+	schedule, err := Parse(cronExpr)
+	if err != nil {
+		return nil, err
+	}
+
+	notBefore := now.In(time.Local)
+	if startAt != nil {
+		start := startAt.In(time.Local)
+		if start.After(notBefore) {
+			notBefore = start
+		}
+	}
+
+	next := schedule.Next(notBefore.Add(-time.Nanosecond)).Round(0)
+	if next.IsZero() {
+		return nil, nil
+	}
+	if endAt != nil && next.After(endAt.In(time.Local)) {
+		return nil, nil
+	}
+
+	return &next, nil
+}
+
+func IsRunAllowed(runAt time.Time, startAt, endAt *time.Time) bool {
+	runAt = runAt.In(time.Local)
+	if startAt != nil && runAt.Before(startAt.In(time.Local)) {
+		return false
+	}
+	if endAt != nil && runAt.After(endAt.In(time.Local)) {
+		return false
+	}
+	return true
+}