feat: run scheduled task ASAP if start is missed

[robotnikz]

Closes #181

Summary

• Adds a "Run as soon as possible if start is missed" checkbox to the schedule UI, visible when the Windows Task Scheduler backend is selected
• When enabled, WinBorg patches the created task via PowerShell to set StartWhenAvailable = true — equivalent to the identically named option in the Windows Task Scheduler GUI
• The PowerShell patch runs after successful schtasks /Create; a failure to patch is logged as a warning but does not fail the overall task creation
• Fully backwards compatible — existing jobs without scheduleRunIfMissed behave as before

Changes

File	What changed
src/types.ts	scheduleRunIfMissed?: boolean added to BackupJob
main/windowsTaskScheduler.js	buildPatchStartWhenAvailableArgs() + PowerShell call in upsertJob
src/components/JobsModal.tsx	Checkbox in Windows Task Scheduler section + state wiring
src/test/windowsTaskScheduler.test.ts	3 new tests (args shape, PowerShell called when true, not called when false)

Test plan

• Create a Windows Task Scheduler job with the new checkbox enabled — verify the task in Windows Task Scheduler UI shows "Run task as soon as possible after a scheduled start is missed" checked
• Create a job with the checkbox disabled — verify the setting is absent
• Set the PC clock past a scheduled time without running — turn the option on, reboot, verify the backup runs on startup
• All 263 unit tests pass