feat: Crontab and Homebrew Services management

[Sean10000]

Summary

• Add Crontab sidebar module: browse, create, edit, enable/disable, and delete user (crontab -l) and system (/etc/crontab) cron jobs with grouped UI matching Launch Agents.
• Add Homebrew Services sidebar module: list, start, stop, and restart brew services for user and system scopes via brew services list --json.
• System-level writes (system crontab, root brew services) reuse existing PrivilegeService admin password prompt, same as system LaunchAgents.

Test plan

• Build and run in Xcode (⌘R)
• Crontab → 用户: create/edit/disable/delete a cron job; verify with crontab -l
• Crontab → 系统: create/edit a system job; confirm admin password prompt; verify /etc/crontab
• Homebrew Services → 用户: start/stop/restart an installed service (e.g. colima); verify with brew services list
• Homebrew Services → 系统: start/stop a service; confirm admin password prompt
• Search works in both new views; sidebar badges update after refresh
• Run unit tests: CrontabParserTests, BrewServicesServiceTests