fix: prevent 500 errors in round-robin scheduling from OOO calibration for single host

[hbjORbj]

What does this PR do?

Fixes 500 error ("Internal Error: Weight filter should never return length=0.") in round-robin scheduling caused by

1. Division by zero in OOO calibration: When a single host has out-of-office entries, the calibration calculation bookingsInTimeframe.length / (hosts.length - 1) causes division by zero

This issues causes NaN to propagate through booking shortfall calculations, resulting in Math.max(...NaN values) = NaN, and the filter user.bookingShortfall === NaN returns an empty array (since NaN !== NaN), triggering the error "Internal Error: Weight filter should never return length=0."

Solutions implemented:

1. OOO calibration guard: Skip OOO calibration when hosts.length <= 1 (conceptually meaningless with a single host)

Mandatory Tasks

• I have self-reviewed the code
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change - N/A (internal bug fix, no API changes)
• I confirm automated tests are in place that prove my fix is effective or that my feature works

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2 Skipped Deployments

Project	Deployment	Preview	Comments	Updated (UTC)
cal	Ignored			Nov 25, 2025 4:34am
cal-eu	Ignored			Nov 25, 2025 4:34am

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