docs: update documentation for v0.4.0 release

- Update README.md with v0.4.0 features and screenshots placeholders
- Update architecture.md with v0.4.0 implementation status
- Update progress.md marking all 27 tasks as completed
- Create CHANGELOG.md with complete release notes
- Add v0.4.0 frontend components and hooks

frontend/src/components/ui/toaster.tsx

@@ -1,44 +1,40 @@
 import { useState, useEffect } from 'react'
+import type { Toast } from './toast-utils'
 
-interface Toast {
-  id: string
-  title?: string
-  description?: string
-  variant?: 'default' | 'destructive'
-}
+type ToastEvent = CustomEvent<Toast>
 
 const Toaster = () => {
   const [toasts, setToasts] = useState<Toast[]>([])
 
   useEffect(() => {
-    const handleToast = (e: CustomEvent<Toast>) => {
-      const toast = { ...e.detail, id: Math.random().toString(36) }
-      setToasts((prev) => [...prev, toast])
+    const handleToast = (e: ToastEvent) => {
+      const toastItem = { ...e.detail, id: Math.random().toString(36) }
+      setToasts((prev) => [...prev, toastItem])
       
       setTimeout(() => {
-        setToasts((prev) => prev.filter((t) => t.id !== toast.id))
+        setToasts((prev) => prev.filter((t) => t.id !== toastItem.id))
       }, 5000)
     }
 
-    window.addEventListener('toast' as any, handleToast)
-    return () => window.removeEventListener('toast' as any, handleToast)
+    window.addEventListener('toast', handleToast as EventListener)
+    return () => window.removeEventListener('toast', handleToast as EventListener)
   }, [])
 
   if (toasts.length === 0) return null
 
   return (
     <div className="fixed bottom-4 right-4 z-50 flex flex-col gap-2">
-      {toasts.map((toast) => (
+      {toasts.map((toastItem) => (
         <div
-          key={toast.id}
+          key={toastItem.id}
           className={`rounded-lg border p-4 shadow-lg ${
-            toast.variant === 'destructive'
+            toastItem.variant === 'destructive'
               ? 'border-destructive bg-destructive text-destructive-foreground'
               : 'border-border bg-background'
           }`}
         >
-          {toast.title && <div className="font-semibold">{toast.title}</div>}
-          {toast.description && <div className="text-sm">{toast.description}</div>}
+          {toastItem.title && <div className="font-semibold">{toastItem.title}</div>}
+          {toastItem.description && <div className="text-sm">{toastItem.description}</div>}
         </div>
       ))}
     </div>
@@ -46,6 +42,3 @@ const Toaster = () => {
 }
 
 export { Toaster }
-export const toast = (props: Omit<Toast, 'id'>) => {
-  window.dispatchEvent(new CustomEvent('toast', { detail: props }))
-}