Add LabelBar datagrid mode

[texodus]

• LabelBar datagrid formatting mode: Adds a new label-bar option to number_fg_mode for numeric columns. Unlike plain bar mode which only renders a proportional fill, label-bar overlays the formatted numeric value on top of the bar using CSS mix-blend-mode: difference for contrast against the fill color.
  
  

• SELECT_ROW_TREE selection mode: Adds a new datagrid edit mode for tree-aware row selection. Available only when group_by is active (non-flat rollup), this mode tracks selections by tree identity rather than flat row index, enabling hierarchical filtering. Introduces a perspective-global-filter event.

• Workspace global filter rework: Replaces the selectable attribute-based master/detail filtering with SELECT_ROW_TREE mode and perspective-global-filter events. Master widgets now restore with edit_mode: "SELECT_ROW_TREE" and detail widgets with READ_ONLY, and event listeners are properly added/removed (fixing leaked bound-function listeners).