feat(17-05): implement serve and schedule commands replacing stubs

- cmd/serve.go: starts scheduler, optionally starts Telegram bot with --telegram flag
- cmd/schedule.go: add/list/remove/run subcommands for scheduled scan job CRUD
- pkg/scheduler/: gocron v2 based scheduler with DB-backed jobs and scan execution
- pkg/storage/scheduled_jobs.go: scheduled_jobs table CRUD with tests
- Remove serve and schedule stubs from cmd/stubs.go

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

pkg/scheduler/source.go

@@ -0,0 +1,21 @@
+package scheduler
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/salvacybersec/keyhunter/pkg/engine/sources"
+)
+
+// selectSchedulerSource returns the appropriate Source for a scheduled scan path.
+// Only file and directory paths are supported (same as bot scans).
+func selectSchedulerSource(path string) (sources.Source, error) {
+	info, err := os.Stat(path)
+	if err != nil {
+		return nil, fmt.Errorf("stat %q: %w", path, err)
+	}
+	if info.IsDir() {
+		return sources.NewDirSource(path), nil
+	}
+	return sources.NewFileSource(path), nil
+}