test(10-04): add failing tests for toast store and ToastContainer

- 6 toast store tests: show/dismiss/auto-dismiss/duration=0/stacking
- 4 ToastContainer tests: empty/render count/click dismiss/accent class
- uses vi.useFakeTimers() for timer-based assertions
- Teleport and AppIcon stubbed for DOM-safe mounting

frontend/src/stores/__tests__/toast.test.js

@@ -0,0 +1,64 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import { setActivePinia, createPinia } from 'pinia'
+import { useToastStore } from '../toast.js'
+
+beforeEach(() => {
+  setActivePinia(createPinia())
+})
+
+afterEach(() => {
+  vi.useRealTimers()
+})
+
+describe('useToastStore', () => {
+  it('show(msg, type, duration) appends a toast with the given fields', () => {
+    const store = useToastStore()
+    store.show('Hi', 'success', 4000)
+    expect(store.toasts.length).toBe(1)
+    expect(store.toasts[0].message).toBe('Hi')
+    expect(store.toasts[0].type).toBe('success')
+    expect(store.toasts[0].duration).toBe(4000)
+  })
+
+  it('show defaults type to success and duration to 4000', () => {
+    const store = useToastStore()
+    store.show('Hi')
+    expect(store.toasts[0].type).toBe('success')
+    expect(store.toasts[0].duration).toBe(4000)
+  })
+
+  it('auto-dismisses after duration using fake timers', () => {
+    vi.useFakeTimers()
+    const store = useToastStore()
+    store.show('Hi', 'success', 4000)
+    expect(store.toasts.length).toBe(1)
+    vi.advanceTimersByTime(4000)
+    expect(store.toasts.length).toBe(0)
+  })
+
+  it('dismiss(id) removes the toast immediately', () => {
+    const store = useToastStore()
+    store.show('Hi', 'success', 0)
+    const id = store.toasts[0].id
+    store.dismiss(id)
+    expect(store.toasts.length).toBe(0)
+  })
+
+  it('duration=0 disables auto-dismiss', () => {
+    vi.useFakeTimers()
+    const store = useToastStore()
+    store.show('Hi', 'success', 0)
+    vi.advanceTimersByTime(10000)
+    expect(store.toasts.length).toBe(1)
+  })
+
+  it('multiple toasts stack with unique ids', () => {
+    const store = useToastStore()
+    store.show('A')
+    store.show('B')
+    store.show('C')
+    expect(store.toasts.length).toBe(3)
+    const ids = store.toasts.map(t => t.id)
+    expect(new Set(ids).size).toBe(3)
+  })
+})