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/storage/schema.sql

@@ -55,3 +55,18 @@ CREATE TABLE IF NOT EXISTS custom_dorks (
 
 CREATE INDEX IF NOT EXISTS idx_custom_dorks_source ON custom_dorks(source);
 CREATE INDEX IF NOT EXISTS idx_custom_dorks_category ON custom_dorks(category);
+
+-- Phase 17: scheduled scan jobs for cron-based recurring scans.
+CREATE TABLE IF NOT EXISTS scheduled_jobs (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    name        TEXT NOT NULL,
+    cron_expr   TEXT NOT NULL,
+    scan_path   TEXT NOT NULL,
+    enabled     INTEGER NOT NULL DEFAULT 1,
+    notify      INTEGER NOT NULL DEFAULT 1,
+    last_run_at DATETIME,
+    next_run_at DATETIME,
+    created_at  DATETIME DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE INDEX IF NOT EXISTS idx_scheduled_jobs_enabled ON scheduled_jobs(enabled);