feat: add SnackbarToast component for canvas feedback

Introduces a singleton snackbar toast component (bottom-center, Teleport
to body) intended for non-blocking canvas feedback. Surfaces an optional
keybinding badge or an action button (e.g. Undo) and supports auto-
dismiss with hover-pause.

Component-only — no app integration in this PR. Wiring to specific
canvas commands (link visibility, focus mode, subgraph unpack) will land
in follow-up PRs once the UX direction is settled (#11718 thread).

Visuals match Figma node 6826:77784 in the Comfy Design System.

Refs FE-484

src/components/graph/SnackbarToast.stories.ts

@@ -0,0 +1,112 @@
+import type { Meta, StoryObj } from '@storybook/vue3-vite'
+
+import Button from '@/components/ui/button/Button.vue'
+import { useSnackbarToast } from '@/composables/useSnackbarToast'
+
+import SnackbarToast from './SnackbarToast.vue'
+
+const meta: Meta<typeof SnackbarToast> = {
+  title: 'Components/Graph/SnackbarToast',
+  component: SnackbarToast,
+  tags: ['autodocs'],
+  parameters: {
+    layout: 'fullscreen'
+  },
+  decorators: [
+    () => ({
+      template:
+        '<div class="relative h-screen bg-base-background p-8"><story /></div>'
+    })
+  ]
+}
+
+export default meta
+type Story = StoryObj<typeof meta>
+
+export const Default: Story = {
+  render: () => ({
+    components: { SnackbarToast, Button },
+    setup() {
+      const toast = useSnackbarToast()
+      function trigger() {
+        toast.show('Toast message')
+      }
+      return { trigger }
+    },
+    template: `
+      <div class="flex flex-col gap-2">
+        <p class="text-base-foreground">Auto-dismiss after 2s. Hover to pause.</p>
+        <Button class="w-fit" @click="trigger">Show toast</Button>
+        <SnackbarToast />
+      </div>
+    `
+  })
+}
+
+export const WithShortcut: Story = {
+  render: () => ({
+    components: { SnackbarToast, Button },
+    setup() {
+      const toast = useSnackbarToast()
+      function trigger() {
+        toast.show('Links hidden', { shortcut: 'Ctrl+A' })
+      }
+      return { trigger }
+    },
+    template: `
+      <div class="flex flex-col gap-2">
+        <p class="text-base-foreground">Toast with assigned keybinding badge.</p>
+        <Button class="w-fit" @click="trigger">Show toast</Button>
+        <SnackbarToast />
+      </div>
+    `
+  })
+}
+
+export const WithUndoAction: Story = {
+  render: () => ({
+    components: { SnackbarToast, Button },
+    setup() {
+      const toast = useSnackbarToast()
+      function trigger() {
+        toast.show('Subgraph unpacked', {
+          actionLabel: 'Undo',
+          onAction: () => {
+            toast.show('Subgraph repacked')
+          }
+        })
+      }
+      return { trigger }
+    },
+    template: `
+      <div class="flex flex-col gap-2">
+        <p class="text-base-foreground">No assigned shortcut: shows an Undo action button.</p>
+        <Button class="w-fit" @click="trigger">Show toast</Button>
+        <SnackbarToast />
+      </div>
+    `
+  })
+}
+
+export const Persistent: Story = {
+  render: () => ({
+    components: { SnackbarToast, Button },
+    setup() {
+      const toast = useSnackbarToast()
+      function trigger() {
+        toast.show('Stays open until dismissed', { duration: 60_000 })
+      }
+      return { trigger, dismiss: toast.dismiss }
+    },
+    template: `
+      <div class="flex flex-col gap-2">
+        <p class="text-base-foreground">Long duration so close-button behavior is testable.</p>
+        <div class="flex gap-2">
+          <Button class="w-fit" @click="trigger">Show toast</Button>
+          <Button class="w-fit" variant="muted-textonly" @click="dismiss">Dismiss</Button>
+        </div>
+        <SnackbarToast />
+      </div>
+    `
+  })
+}

src/components/graph/SnackbarToast.vue

@@ -0,0 +1,74 @@
+<template>
+  <Teleport to="body">
+    <div
+      v-if="visible"
+      role="status"
+      aria-live="polite"
+      class="fixed bottom-16 left-1/2 z-1000 flex -translate-x-1/2 items-center gap-4 rounded-lg bg-base-foreground py-1 pr-2 pl-3 text-sm text-base-background shadow-[1px_1px_8px_0_rgba(0,0,0,0.4)]"
+      @mouseenter="pause"
+      @mouseleave="startTimer"
+    >
+      <span class="truncate">
+        {{ message }}
+      </span>
+      <kbd
+        v-if="shortcut"
+        class="flex h-4 min-w-3.5 items-center justify-center rounded-sm bg-base-background/70 px-1 text-xs font-normal text-base-foreground"
+      >
+        {{ shortcut }}
+      </kbd>
+      <ToolbarRoot
+        orientation="horizontal"
+        :aria-label="t('g.dismiss')"
+        class="flex items-center pl-2"
+      >
+        <ToolbarButton v-if="hasAction" as-child @click="handleAction">
+          <Button
+            variant="inverted"
+            size="md"
+            class="text-sm hover:bg-base-foreground/80"
+          >
+            {{ actionLabel }}
+          </Button>
+        </ToolbarButton>
+        <ToolbarButton as-child @click="dismiss">
+          <Button
+            variant="inverted"
+            size="md"
+            :aria-label="t('g.dismiss')"
+            class="hover:bg-base-foreground/80"
+          >
+            <i class="icon-[lucide--x] size-4" />
+          </Button>
+        </ToolbarButton>
+      </ToolbarRoot>
+    </div>
+  </Teleport>
+</template>
+
+<script setup lang="ts">
+import { ToolbarButton, ToolbarRoot } from 'reka-ui'
+import { computed } from 'vue'
+import { useI18n } from 'vue-i18n'
+
+import Button from '@/components/ui/button/Button.vue'
+import { useSnackbarToast } from '@/composables/useSnackbarToast'
+
+const { t } = useI18n()
+const {
+  message,
+  shortcut,
+  visible,
+  actionLabel,
+  onAction,
+  dismiss,
+  pause,
+  startTimer
+} = useSnackbarToast()
+
+const hasAction = computed(() => !!onAction.value && !shortcut.value)
+
+function handleAction() {
+  onAction.value?.()
+}
+</script>

src/composables/useSnackbarToast.ts

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+import { ref } from 'vue'
+
+const message = ref('')
+const shortcut = ref('')
+const visible = ref(false)
+const actionLabel = ref('')
+const onAction = ref<(() => void) | null>(null)
+let timeout: ReturnType<typeof setTimeout> | null = null
+let duration = 2000
+
+export function useSnackbarToast() {
+  function show(
+    msg: string,
+    options?: {
+      shortcut?: string
+      duration?: number
+      actionLabel?: string
+      onAction?: () => void
+    }
+  ) {
+    if (timeout) clearTimeout(timeout)
+    message.value = msg
+    shortcut.value = options?.shortcut ?? ''
+    actionLabel.value = options?.actionLabel ?? ''
+    onAction.value = options?.onAction ?? null
+    duration = options?.duration ?? 2000
+    visible.value = true
+    startTimer()
+  }
+
+  function startTimer() {
+    if (timeout) clearTimeout(timeout)
+    timeout = setTimeout(() => {
+      visible.value = false
+    }, duration)
+  }
+
+  function pause() {
+    if (timeout) clearTimeout(timeout)
+  }
+
+  function dismiss() {
+    if (timeout) clearTimeout(timeout)
+    visible.value = false
+  }
+
+  return {
+    message,
+    shortcut,
+    visible,
+    actionLabel,
+    onAction,
+    show,
+    dismiss,
+    pause,
+    startTimer
+  }
+}