Dropdown/picker closed-state display. Same label-above-input shape
as add_form_field_v0 with:
- always-present trailing chevron-down icon
- when `value` is set: black value text + chevron
- when absent: placeholder text styled gray (#94A3B8) + chevron
- justifyContent=space_between pushes the chevron to the right edge
Explicitly NOT modeled: open-menu state (dropdown list). An open
dropdown needs absolute positioning + scrim + per-option states
that belong in a different builder; compose via batch_design for now.
Wired across all three paths + elements.md keyword map + examples.
Tests:
- pen-mcp: 7 new cases (value/placeholder rendering, custom
trailing_icon, required suffix, id uniqueness, parent_id rollback)
- Parametric coverage: auto-extended (+1 case each in 9 files).
Total delta: 2955 → 2979 passing.
Closes#48; covers part of #50 (select entry).
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