feat: F025 button & action logic audit — global toast, confirm dialog, wired mutations

- Add ToastProvider (global MUI Snackbar stack) + toastStore (Zustand)
- Add ConfirmDialog reusable component for destructive actions
- Wire toast feedback to all async mutations: review status, AI output status,
  match approval, shortlist add/remove/title/finalize, signal review actions
- Fix dead UserMenu buttons (Profil, Einstellungen) — show info toast
- Migrate local Snackbar instances in AddToShortlistDialog and
  FutureSignalDetailPanel to global toast store

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/stores/toastStore.ts

@@ -0,0 +1,27 @@
+import { create } from 'zustand'
+
+export type ToastSeverity = 'success' | 'error' | 'warning' | 'info'
+
+export interface ToastMessage {
+  id: string
+  message: string
+  severity: ToastSeverity
+  duration?: number
+}
+
+interface ToastState {
+  toasts: ToastMessage[]
+  showToast: (message: string, severity?: ToastSeverity, duration?: number) => void
+  dismissToast: (id: string) => void
+}
+
+export const useToastStore = create<ToastState>((set) => ({
+  toasts: [],
+  showToast: (message, severity = 'success', duration = 4000) => {
+    const id = crypto.randomUUID()
+    set((s) => ({ toasts: [...s.toasts, { id, message, severity, duration }] }))
+  },
+  dismissToast: (id) => {
+    set((s) => ({ toasts: s.toasts.filter((t) => t.id !== id) }))
+  },
+}))