- Add CompletionHistorySheet for viewing task completion history (Android & iOS)
- Update TaskCard and DynamicTaskCard with completion history access
- Add getTaskCompletions API endpoint to TaskApi and APILayer
- Update models (CustomTask, Document, TaskCompletion, User) for Go API alignment
- Improve TaskKanbanView with completion history integration
- Update iOS TaskViewModel with completion history loading
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Co-Authored-By: Claude <noreply@anthropic.com>