[imports] Restyle CSV import modals and fix task type metadata matching

[frankrousseau]

Problem

• The CSV import and preview modals were stuck at 640px, with raw column lists, a bulky legend and dead scoped width styles
• On task type pages the preview offered the entity metadata descriptors instead of those of the current task type (route sniffing matched the entity segment first)

Solution

• Widen both modals, present column hints and legend as compact info panels, reuse the shared upload drop zone and switch the paste area to monospace
• Match task-types routes first, filter Task descriptors on the current task type, and list metadata columns in the task type import modal (server side handled in [import] Handle person and task metadata in CSV imports zou#1181)