feat(canvas): 下拉统一换成 SelectMenu 组件并支持向上展开

frontend/src/components/SelectMenu.vue

@@ -13,6 +13,7 @@ const props = defineProps({
   placeholder: { type: String, default: '请选择' },
   mono: { type: Boolean, default: false },
   disabled: { type: Boolean, default: false },
+  up: { type: Boolean, default: false }, // 面板向上展开(底部居中的输入框用)
 })
 const emit = defineEmits(['update:modelValue'])
 
@@ -90,8 +91,9 @@ onUnmounted(() => document.removeEventListener('mousedown', onDocClick))
       leave-from-class="opacity-100 translate-y-0"
       leave-to-class="opacity-0 -translate-y-1">
       <div v-if="open" ref="panel"
-           class="absolute z-30 mt-2 w-full max-h-64 overflow-auto rounded-xl border border-[color:var(--glass-border)]
-                  bg-[var(--menu-bg)] backdrop-blur-xl p-1.5 shadow-[var(--glass-shadow-lg)]">
+           class="absolute z-30 w-full max-h-64 overflow-auto rounded-xl border border-[color:var(--glass-border)]
+                  bg-[var(--menu-bg)] backdrop-blur-xl p-1.5 shadow-[var(--glass-shadow-lg)]"
+           :class="up ? 'bottom-full mb-2' : 'mt-2'">
         <button v-for="(o, i) in options" :key="o.value" type="button"
                 :data-idx="i" @click="pick(o)" @mouseenter="active = i"
                 class="w-full flex items-center justify-between gap-2 rounded-lg px-3 py-2 text-left text-sm font-medium transition-colors"