[turinglambdaai]

Parity and data correctness

Windows now supports multi-select and batch complete/move (#41, #42) but cannot schedule several tasks at once. Separately, the single-task Clear Date action sets due_date = null yet retains an invisible due_time; Linux already clears both. This PR addresses both deficiencies.

Changes

• Add a localized Schedule Selected / 批量排期 button to the contextual multi-selection toolbar, with Today, Tomorrow and Clear options.
• Capture the selected task IDs at flyout opening. Dispatch existing SetTaskDueAsync for each captured ID, avoiding wrong targets if the view refreshes or selection changes during the popup.
• When clearing a due date (individual or batch), also clear the associated due time. Preserve task owner, text, notes, completion status and other untouched fields.
• Extend Windows packaged accessibility acceptance to check the batch schedule action is enabled for two selected tasks; the full mutation roundtrip needs manual/extended E2E verification.
• Update cross-platform UX benchmark and zh/en localization.

Dependencies

Stacked on #42 → #41 → #39 → #36 → #35 → #32. Integrate bottom-up and repeat the combined three-platform build/acceptance suite after merging.

Manual QA / release gate

• WinUI x64 compile and packaged Product Acceptance green
• Select two tasks in 生活 → Schedule → Tomorrow → both show tomorrow without moving lists
• Assign different due times; Clear on both → due dates and times empty after restart
• Change selection while menu is open: command acts only on the snapshot of selected IDs
• Global search across 工作/生活: schedule targets real task IDs from both lists
• UI text in zh/en; 100/150% DPI; mouse and keyboard paths

Not included: bulk delete with undo or Windows inline detail editor; those remain unfulfilled. Do not release based on this PR alone.