Redesign FilledDropdown component to match prototype design

[guiyanakuang]

Redesign the FilledDropdown component to match the Pencil prototype (Dropdown1).

Changes

• Replace heavy ExposedDropdownMenuBox + BasicTextField + TextFieldDefaults.DecorationBox with a compact Surface trigger + DropdownMenu
• Use rounded rectangle (8dp) with 1dp outline border, matching Counter component style
• Compact sizing: 13sp font, 14dp icon, minimal padding (10dp horizontal, 6dp vertical)
• Fix hover/ripple shape to clip to rounded corners
• Set containerColor and shape on DropdownMenu to match trigger, eliminating edge color mismatch
• Compact menu items with fixed 32dp height and matching padding
• Selected item indicated by primary-colored text + check icon
• Replace manual text width measurement with intrinsic sizing
• Use AppUISize constants throughout