1. Attendance form: Force start date to blank by clearing Django 5.x auto-fill
from model default (default=timezone.now). Added self.fields['date'].initial=None
in AttendanceLogForm.__init__().
2. History list view: When filtering by a specific worker, show only that
worker's name in the Workers column (not all workers on the log). Uses
filtered_worker_obj passed from the view.
3. History list view: Added Amount column (admin-only) showing daily cost.
When filtering by worker, shows that worker's daily_rate. When unfiltered,
shows total via new WorkLog.display_amount property (sum of all workers'
daily_rate, uses prefetch cache for efficiency).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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