Description Modal In progress

Terminal description modal (1:1 from description-modal-spec). Single-textarea note entry — NbNavShell header (#35325E, Receipt label) + textarea + Cancel/Save buttons. 3 states (empty placeholder / writing: blue border + focus ring + blinking caret / filled value) × 2 sizes (S 500 / M 600, content padding 12→16, textarea min-height 104→148). Save has leading check. Radius 8px, Inter, all colours/space/type bound to design tokens.