Unit tests for QML Cards, Workflow, System, and Visualization components #361

Part of #356

Add unit tests in tests/qml/ for cards, workflow handlers, system widgets, and charts:

• ProjectDetailsCard.qml (project info, status badge, progress)
• ActivityDetailsCard.qml (activity details, assignee, due date)
• UpdatesDetailsCard.qml (update summary and timestamp)
• FormDraftHandler.qml (draft autosave and change tracking)
• AttachmentManager.qml (attachment list and file deletion signal)
• VoiceTimerWidget.qml (voice recording states and timer controls)
• ModelDownloadTimerWidget.qml (download progress and cancel button)
• ImagePreviewer.qml (image zoom, pan, close action)
• BackendBridge.qml (signal dispatch between QML and Python)
• EHowerIndicator.qml (dot coordinate placement in Eisenhower matrix)
• EHower.qml (matrix 2x2 grid layout)
• ProjectPieChart.qml (pie slice angles and empty state)
• ProjectList.qml (list model population and selection)

Note: TasksForDayWidget, CreateUpdatePage, and Bubblemap are unused and scheduled for removal in #367.