2. `customFilterDropdown` Prop

[MitchellShiell]

Goal
Define and expose a customFilterDropdowns prop on DictionaryTableViewer. Each entry in the array specifies a display label and a dot-path to a property within each schema's meta object. Thread this prop through to the components that need it (Toolbar, filter logic, accordion).

Example shape from discussed spec (just for reference update at your own discretion):

customFilterDropdowns?: Array<{
  label: string;
  filterProperty: string; // dot-path e.g. 'meta.tags.submitter_type'
}>

Acceptance Criteria

• customFilterDropdowns is an optional prop on DictionaryTableViewer
• When omitted, existing behaviour is entirely unchanged
• The prop is correctly typed and exported so consuming applications can reference the type
• The prop is threaded to wherever filter values will need to be read (Toolbar, schema filter logic)