fix(cron): restore management actions after scan result change

[Linxiushen]

Summary

• restore manage_cron status, list, and manual-run actions after the scan_jobs() return contract expanded
• unpack (valid_jobs, invalid_mtimes) at each direct management consumer while leaving invalid-file tracking with the scheduler
• add focused regression coverage for status rendering, disabled-job filtering, and manual execution lookup

Root cause

scan_jobs() now returns (valid_jobs, invalid_mtimes), but these three consumers still treated the complete tuple as List[CronJob]. They consequently attempted to read CronJob attributes from the tuple's list or dictionary members and returned caught AttributeError failures.

Testing

• targeted pytest: 4 passed (test_manage_cron_scan_result.py and test_cron_model_payload.py)
• Ruff check and format check on the new test file
• Python bytecode compilation for the changed source and test files
• git diff --check

Fixes #88