feat: enhance project management with duplicate name checks and toast notifications

- Added duplicate name check in NewProjectDialog to warn users of existing project names.
- Integrated toast notifications for actions like project deletion and export in ProjectsPage.
- Implemented project ordering and restoration functionality in platform context.
- Updated ProjectsPage to include search, sorting, and pagination features.
- Created a new Toast component for displaying notifications with optional undo actions.
- Refactored main application entry to include ToastProvider for global toast management.

frontend/src/components/ui/toast.tsx

@@ -0,0 +1,111 @@
+/**
+ * Simple toast: message + optional Undo action. Auto-dismisses after a delay.
+ */
+
+import React, { createContext, useCallback, useContext, useState } from 'react'
+import { cn } from '@/lib/utils'
+
+export type ToastItem = {
+  id: string
+  message: string
+  undo?: () => void
+}
+
+type ToastContextValue = {
+  toasts: ToastItem[]
+  addToast: (message: string, options?: { undo?: () => void; duration?: number }) => void
+  removeToast: (id: string) => void
+}
+
+const ToastContext = createContext<ToastContextValue | null>(null)
+
+const TOAST_DURATION = 5000
+
+export function ToastProvider({ children }: { children: React.ReactNode }) {
+  const [toasts, setToasts] = useState<ToastItem[]>([])
+  const timersRef = React.useRef<Record<string, ReturnType<typeof setTimeout>>>({})
+
+  const removeToast = useCallback((id: string) => {
+    setToasts((prev) => prev.filter((t) => t.id !== id))
+    const t = timersRef.current[id]
+    if (t) {
+      clearTimeout(t)
+      delete timersRef.current[id]
+    }
+  }, [])
+
+  const addToast = useCallback(
+    (message: string, options?: { undo?: () => void; duration?: number }) => {
+      const id = `toast-${Date.now()}-${Math.random().toString(36).slice(2)}`
+      const duration = options?.duration ?? TOAST_DURATION
+      setToasts((prev) => [...prev, { id, message, undo: options?.undo }])
+      const timer = setTimeout(() => removeToast(id), duration)
+      timersRef.current[id] = timer
+    },
+    [removeToast]
+  )
+
+  return (
+    <ToastContext.Provider value={{ toasts, addToast, removeToast }}>
+      {children}
+      <ToastViewport toasts={toasts} removeToast={removeToast} />
+    </ToastContext.Provider>
+  )
+}
+
+function ToastViewport({
+  toasts,
+  removeToast,
+}: {
+  toasts: ToastItem[]
+  removeToast: (id: string) => void
+}) {
+  if (toasts.length === 0) return null
+  return (
+    <div
+      className="fixed bottom-4 right-4 z-[100] flex max-w-[420px] flex-col gap-2"
+      role="region"
+      aria-label="Notifications"
+    >
+      {toasts.map((t) => (
+        <div
+          key={t.id}
+          className={cn(
+            'flex items-center justify-between gap-3 rounded-lg border bg-background px-4 py-3 text-sm shadow-lg',
+            'animate-in slide-in-from-bottom-2 fade-in-0'
+          )}
+        >
+          <span className="flex-1">{t.message}</span>
+          <div className="flex shrink-0 gap-2">
+            {t.undo && (
+              <button
+                type="button"
+                className="font-medium text-primary underline-offset-4 hover:underline"
+                onClick={() => {
+                  t.undo?.()
+                  removeToast(t.id)
+                }}
+              >
+                Undo
+              </button>
+            )}
+            <button
+              type="button"
+              className="text-muted-foreground hover:text-foreground"
+              onClick={() => removeToast(t.id)}
+              aria-label="Dismiss"
+            >
+              ×
+            </button>
+          </div>
+        </div>
+      ))}
+    </div>
+  )
+}
+
+export function useToast() {
+  const ctx = useContext(ToastContext)
+  if (!ctx) throw new Error('useToast must be used within ToastProvider')
+  return ctx
+}