feat(component): add SongScrim and message toast

src/components/SongMessageContainer.vue

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+<script setup lang="ts">
+/* SongMessageContainer — 提示框承载层（雾隐淡入，墨线 + 小章意象） */
+interface ToastItem {
+  id: number
+  type: string
+  text: string
+}
+
+defineProps<{
+  list: ToastItem[]
+}>()
+</script>
+
+<template>
+  <div class="song-messages">
+    <TransitionGroup name="song-toast">
+      <div v-for="t in list" :key="t.id" class="song-toast" :class="`song-toast--${t.type}`">
+        <span class="song-toast__stamp" aria-hidden="true">
+          <template v-if="t.type === 'success'">✓</template>
+          <template v-else-if="t.type === 'danger'">✕</template>
+          <template v-else-if="t.type === 'warning'">!</template>
+          <template v-else>印</template>
+        </span>
+        <span class="song-toast__text">{{ t.text }}</span>
+      </div>
+    </TransitionGroup>
+  </div>
+</template>
+
+<style scoped>
+.song-messages {
+  position: fixed;
+  top: 24px;
+  left: 50%;
+  transform: translateX(-50%);
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 10px;
+  z-index: 1000;
+  pointer-events: none;
+}
+
+.song-toast {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  max-width: min(90vw, 420px);
+  padding: 10px 18px;
+  background: var(--song-bg-elevated);
+  border: 1px solid var(--song-border);
+  border-left: 3px solid var(--song-text-secondary);
+  border-radius: var(--song-radius-s);
+  box-shadow: var(--song-shadow-2);
+  color: var(--song-text);
+  font-size: 13px;
+  pointer-events: auto;
+}
+
+.song-toast__stamp {
+  display: grid;
+  place-items: center;
+  width: 18px;
+  height: 18px;
+  flex-shrink: 0;
+  border: 1px solid currentColor;
+  border-radius: 2px;
+  font-size: 11px;
+  line-height: 1;
+  font-weight: 700;
+  color: var(--song-text-secondary);
+}
+
+.song-toast.song-toast--success { border-left-color: var(--song-success); }
+.song-toast.song-toast--success .song-toast__stamp { color: var(--song-success); }
+.song-toast.song-toast--danger { border-left-color: var(--song-danger); }
+.song-toast.song-toast--danger .song-toast__stamp { color: var(--song-danger); }
+.song-toast.song-toast--warning { border-left-color: var(--song-warning); }
+.song-toast.song-toast--warning .song-toast__stamp { color: var(--song-warning); }
+.song-toast.song-toast--info { border-left-color: var(--song-primary); }
+.song-toast.song-toast--info .song-toast__stamp { color: var(--song-primary); }
+
+/* 雾隐淡入 §7 */
+.song-toast-enter-active,
+.song-toast-leave-active {
+  transition: opacity var(--song-dur-2) var(--song-ease),
+    transform var(--song-dur-2) var(--song-ease);
+}
+
+.song-toast-enter-from,
+.song-toast-leave-to {
+  opacity: 0;
+  transform: translateY(-10px);
+}
+</style>

src/components/SongScrim.vue

@@ -0,0 +1,115 @@
+<script setup lang="ts">
+/* SongScrim — 纹样底纹合成器 §5
+ * 纹样均以 SVG 几何化矢量、低占比，置于内容之下。
+ * pattern: ice(冰裂纹) | blind(直棂窗) | tortoise(龟背纹) | vine(缠枝纹) |
+ *          water(水波) | cloud(祥云)
+ * box: 卡片/区块内局部底纹 */
+withDefaults(
+  defineProps<{
+    pattern?: 'ice' | 'blind' | 'tortoise' | 'vine' | 'water' | 'cloud'
+    opacity?: number
+    box?: boolean
+  }>(),
+  { pattern: 'ice', opacity: 1, box: false }
+)
+defineOptions({ name: 'SongScrim' })
+
+const PATTERNS: Record<string, string> = {
+  ice: `
+    <svg xmlns="http://www.w3.org/2000/svg" width="220" height="220" viewBox="0 0 220 220">
+      <g fill="none" stroke="#6B7A86" stroke-width="1">
+        <path d="M0 40 40 0 M60 0 0 60 M40 40 90 90 M90 90 110 70 M0 90 90 0"/>
+        <path d="M120 0 90 30 M0 120 30 90 M110 110 60 160 M160 60 110 110 M90 90 160 160"/>
+        <path d="M220 40 180 0 M180 180 220 220 M40 220 0 180 M180 180 160 200 M200 160 180 180"/>
+      </g>
+    </svg>`,
+  blind: `
+    <svg xmlns="http://www.w3.org/2000/svg" width="120" height="120" viewBox="0 0 120 120">
+      <g fill="none" stroke="#6B7A86" stroke-width="1">
+        <path d="M0 0v120 M20 0v120 M40 0v120 M60 0v120 M80 0v120 M100 0v120 M120 0v120"/>
+      </g>
+    </svg>`,
+  tortoise: `
+    <svg xmlns="http://www.w3.org/2000/svg" width="120" height="120" viewBox="0 0 120 120">
+      <g fill="none" stroke="#6B7A86" stroke-width="1">
+        <path d="M30 8 60 21 30 34Z M60 21 90 8 90 34Z"/>
+        <path d="M30 34 60 60 30 86Z M60 60 90 34 90 86Z"/>
+        <path d="M30 8 30 60 0 38Z M90 8 90 60 120 38Z"/>
+        <path d="M30 86 0 64 0 92Z M90 86 120 64 120 92Z"/>
+      </g>
+    </svg>`,
+  vine: `
+    <svg xmlns="http://www.w3.org/2000/svg" width="120" height="60" viewBox="0 0 120 60">
+      <g fill="none" stroke="#6B7A86" stroke-width="1">
+        <path d="M0 30 Q15 10 30 30 T60 30 T90 30 T120 30"/>
+        <path d="M10 45 q0 -12 0 -24 M30 45 30 15 M50 45 50 15 M70 45 70 15 M90 45 90 15 M110 45 110 15"/>
+      </g>
+    </svg>`,
+  water: `
+    <svg xmlns="http://www.w3.org/2000/svg" width="120" height="120" viewBox="0 0 120 120">
+      <g fill="none" stroke="#6B7A86" stroke-width="1">
+        <path d="M20 40 q10 -8 20 0 q10 8 20 0 q10 -8 20 0 q10 8 20 0"/>
+        <path d="M10 64 q10 -8 20 0 q10 8 20 0 q10 -8 20 0 q10 8 20 0 q10 -8 20 0"/>
+        <path d="M30 88 q10 -8 20 0 q10 8 20 0 q10 -8 20 0"/>
+        <path d="M5 16 q10 -8 20 0 q10 8 20 0 q10 -8 20 0 q10 8 20 0 q10 -8 20 0 q10 8 20 0"/>
+      </g>
+    </svg>`,
+  cloud: `
+    <svg xmlns="http://www.w3.org/2000/svg" width="120" height="120" viewBox="0 0 120 120">
+      <g fill="none" stroke="#6B7A86" stroke-width="1">
+        <path d="M10 30 C10 12 30 8 34 24 C38 6 62 10 58 28 C78 18 90 34 76 46 C96 46 96 66 72 62 C82 78 60 88 54 74 C52 92 30 92 28 74 C12 84 2 68 18 60 C0 54 2 38 22 44 C14 34 16 18 30 24 C22 26 14 26 10 30 Z"/>
+      </g>
+    </svg>`
+}
+</script>
+
+<template>
+  <div class="song-scrim" :class="{ 'song-scrim--box': box }" aria-hidden="true">
+    <div
+      v-for="i in 4"
+      :key="i"
+      class="song-scrim__tile"
+      v-html="PATTERNS[pattern]"
+      :style="{ opacity }"
+    />
+  </div>
+</template>
+
+<style scoped>
+:global(.song-scrim) {
+  position: fixed;
+  inset: 0;
+  z-index: 0;
+  pointer-events: none;
+  overflow: hidden;
+  display: grid;
+  grid-template-columns: repeat(2, 1fr);
+  grid-template-rows: repeat(2, 1fr);
+}
+
+.song-scrim--box {
+  position: absolute !important;
+  border-radius: var(--song-radius-l);
+}
+
+.song-scrim__tile {
+  width: 100%;
+  height: 100%;
+}
+
+.song-scrim__tile :deep(svg) {
+  width: 100%;
+  height: 100%;
+}
+
+/* 纹样线条颜色由 --song-scrim-line 按主题决定（低对比、确定性渲染，不用 blend/filter 技巧） */
+.song-scrim__tile :deep(path),
+.song-scrim__tile :deep(line),
+.song-scrim__tile :deep(circle) {
+  stroke: var(--song-scrim-line, rgba(90, 107, 116, 0.16));
+}
+
+.song-scrim--box :deep(svg) {
+  opacity: 0.5;
+}
+</style>

src/composables/useMessage.ts

@@ -0,0 +1,44 @@
+import { createVNode, reactive, render } from 'vue'
+import SongMessageContainer from '@/components/SongMessageContainer.vue'
+
+interface ToastItem {
+  id: number
+  type: string
+  text: string
+}
+
+type ToastType = 'success' | 'danger' | 'warning' | 'info'
+
+const list = reactive<ToastItem[]>([])
+let seed = 0
+let hostEl: HTMLDivElement | null = null
+
+function remove(id: number) {
+  const i = list.findIndex((t) => t.id === id)
+  if (i > -1) list.splice(i, 1)
+}
+
+function push(type: ToastType, text: string, duration = 3400) {
+  const id = ++seed
+  list.push({ id, type, text })
+  setTimeout(() => remove(id), duration)
+}
+
+function ensureHost() {
+  if (!hostEl) {
+    hostEl = document.createElement('div')
+    hostEl.className = 'song-message-host'
+    document.body.appendChild(hostEl)
+    render(createVNode(SongMessageContainer, { list }), hostEl)
+  }
+}
+
+export function useMessage() {
+  ensureHost()
+  return {
+    success: (text: string) => push('success', text),
+    danger: (text: string) => push('danger', text),
+    warning: (text: string) => push('warning', text),
+    info: (text: string) => push('info', text)
+  }
+}