Fix: workspace management, undo/redo button states, and import/export

[rebmoreno]

Summary

This PR fixes several bugs introduced after the UI restructure merge and adds improvements to the workspace.

Changes

• Clear Workspace — metadata and refresh buttons now reset to their true default state (grey background, correct icon and text)
• Undo/Redo button states — metadata and refresh button colors now correctly restore on undo/redo using tracked state variables (metadataStateValue, refreshStateValue) instead of reading inline styles from the DOM, which was unreliable due to browser color normalization
• Date bounds display — earliest/latest date labels now restore correctly on undo instead of showing MM/DD/YY
• Date range modal — fixed broken prescalerInput line that was silently stopping execution and preventing Retrieve Data from working
• Packet refresh listener — event listener is now correctly re-attached or removed on undo/redo to match the restored refresh state
• Export timestamp — workspace export filename now uses local date instead of UTC
• Import safety — added fallback defaults for metadataState, refreshState, and canRefresh when importing older workspace files that don't have these fields
• Database Button - Changes to device name rather than Database name

Testing

• Select a dataset and verify metadata and refresh button colors appear correctly
• Use undo/redo and verify button colors restore correctly
• Clear workspace and verify all buttons reset to default grey
• Use date range modal and verify Retrieve Data works
• Export a workspace and verify filename date matches local date
• Import an old workspace file and verify it loads without errors