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>

go.sum

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