feat(ui): 계좌/분류 선택을 바텀시트로 (정기결제 폼)

- BottomSheet.vue: 아래에서 올라오는 콘텐츠 높이 시트(재사용)
- SheetSelect.vue: 필드형 트리거 → 바텀시트 단일 선택(계좌/카드)
- 정기결제 폼: 계좌는 SheetSelect, 분류는 트리거 → 시트 안 CategoryPicker
  (선택 전에는 목록 미노출, 선택 시 값 채움)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/ui/SheetSelect.vue

@@ -0,0 +1,113 @@
+<script setup>
+// 필드형 트리거를 누르면 바텀시트로 옵션을 보여주고 단일 선택. (계좌·카드 선택 등)
+import { computed, ref } from 'vue'
+import BottomSheet from './BottomSheet.vue'
+
+const props = defineProps({
+  modelValue: { type: [String, Number], default: '' },
+  options: { type: Array, default: () => [] }, // [{ value, label }]
+  placeholder: { type: String, default: '선택하세요' },
+  title: { type: String, default: '선택' },
+  disabled: { type: Boolean, default: false },
+  emptyText: { type: String, default: '선택할 항목이 없습니다' },
+})
+const emit = defineEmits(['update:modelValue'])
+
+const open = ref(false)
+const selected = computed(() => props.options.find((o) => o.value === props.modelValue) || null)
+function pick(o) {
+  emit('update:modelValue', o.value)
+  open.value = false
+}
+</script>
+
+<template>
+  <button
+    type="button" class="ss-trigger" :class="{ empty: !selected }"
+    :disabled="disabled" @click="open = true"
+  >
+    <span class="ss-label">{{ selected ? selected.label : placeholder }}</span>
+    <span class="ss-caret">▾</span>
+  </button>
+
+  <BottomSheet v-model="open" :title="title">
+    <ul v-if="options.length" class="ss-list">
+      <li v-for="o in options" :key="o.value">
+        <button
+          type="button" class="ss-opt" :class="{ active: o.value === modelValue }"
+          @click="pick(o)"
+        >
+          <span>{{ o.label }}</span>
+          <span v-if="o.value === modelValue" class="ss-check">✓</span>
+        </button>
+      </li>
+    </ul>
+    <p v-else class="ss-empty">{{ emptyText }}</p>
+  </BottomSheet>
+</template>
+
+<style scoped>
+.ss-trigger {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 0.5rem;
+  width: 100%;
+  padding: 0.55rem 0.75rem;
+  border: 1px solid var(--color-border);
+  border-radius: 6px;
+  background: var(--color-background-soft);
+  color: var(--color-text);
+  font-size: 0.9rem;
+  cursor: pointer;
+  text-align: left;
+}
+.ss-trigger:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+}
+.ss-trigger.empty .ss-label {
+  opacity: 0.5;
+}
+.ss-label {
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.ss-caret {
+  opacity: 0.5;
+  font-size: 0.8rem;
+  flex-shrink: 0;
+}
+.ss-list {
+  list-style: none;
+  margin: 0;
+  padding: 0;
+}
+.ss-opt {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  width: 100%;
+  padding: 0.85rem 0.4rem;
+  border: 0;
+  border-bottom: 1px solid var(--color-border);
+  background: transparent;
+  color: var(--color-text);
+  font-size: 0.95rem;
+  cursor: pointer;
+  text-align: left;
+}
+.ss-opt.active {
+  color: hsla(160, 100%, 37%, 1);
+  font-weight: 700;
+}
+.ss-check {
+  color: hsla(160, 100%, 37%, 1);
+}
+.ss-empty {
+  padding: 1.2rem 0.4rem;
+  opacity: 0.6;
+  text-align: center;
+}
+</style>