feat(shift_type): add configurable option to mark absent on same day

[iamkhanraheel]

Reason

• There was no way to mark Absent on the same day, the system always waited until the next day, regardless of when the shift's checkout window closed.
• This hardcoded 1-day wait had no way to opt out, delaying attendance review/correction until the following day

Changes Done

• Added an Absent Buffer (Days) field on Shift Type (default 1 — existing behavior unchanged unless changed). Set to 0 to mark Absent the same day, or any higher number for a longer buffer.
• Setting it to 0 requires Automatically update Last Sync of Checkin too; validated on save, since same-day marking depends on it.
• get_start_and_end_dates() now uses this configurable buffer instead of a hardcoded 1-day wait.

Closes: #5082

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge within the scope of this follow-up review.

_{Reviews (6) · Last reviewed commit: "Merge remote-tracking branch 'upstream/d..."}

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[asmitahase]

add screenshots/videos

[github-actions]

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