Add global app banners and integrate into layout

Introduce a global app banners store (GUI/src/stores/appBanners.ts) and switch authentication error/notification flows to use it. GUI/src/Layout.vue now consumes the banner store, replaces the single snackbar with a stacked, dismissible banner UI (styles, transitions and z-index included), and adds navigateToBrandTarget() to route the brand button based on auth state. GUI/src/routes/authentication/Login.vue was updated to push errors to the new banner store and remove the local alert. Minor route adjustments in GUI/src/plugins/routesLayout.ts: rename 'Dash' to 'Dashboard' and change Login visibility to Unauthenticated. codexInfo.md updated to document these UI/behavior changes.

GUI/src/stores/appBanners.ts

@@ -0,0 +1,82 @@
+import { ref } from 'vue'
+import { defineStore } from 'pinia'
+
+export type AppBannerType = 'success' | 'info' | 'warning' | 'error'
+
+export interface AppBannerMessage {
+  id: string
+  type: AppBannerType
+  title?: string
+  message: string
+  createdAt: number
+}
+
+interface PushBannerInput {
+  type?: AppBannerType
+  title?: string
+  message: string
+}
+
+const MAX_BANNERS = 8
+
+function createBannerId() {
+  if (typeof crypto !== 'undefined' && typeof crypto.randomUUID === 'function') {
+    return crypto.randomUUID()
+  }
+
+  return `banner-${Date.now()}-${Math.random().toString(36).slice(2, 9)}`
+}
+
+export const useAppBannersStore = defineStore('app-banners', () => {
+  const banners = ref<AppBannerMessage[]>([])
+
+  function push(input: PushBannerInput) {
+    const now = Date.now()
+    const type = input.type ?? 'info'
+    const normalizedMessage = input.message.trim()
+    if (normalizedMessage.length === 0) {
+      return ''
+    }
+
+    const lastBanner = banners.value[banners.value.length - 1]
+    if (
+      lastBanner &&
+      lastBanner.type === type &&
+      lastBanner.message === normalizedMessage &&
+      now - lastBanner.createdAt < 1200
+    ) {
+      return lastBanner.id
+    }
+
+    const banner: AppBannerMessage = {
+      id: createBannerId(),
+      type,
+      title: input.title,
+      message: normalizedMessage,
+      createdAt: now,
+    }
+
+    banners.value = [...banners.value, banner].slice(-MAX_BANNERS)
+    return banner.id
+  }
+
+  function pushError(message: string, title = 'Fehler') {
+    return push({ type: 'error', title, message })
+  }
+
+  function dismiss(id: string) {
+    banners.value = banners.value.filter((banner) => banner.id !== id)
+  }
+
+  function clear() {
+    banners.value = []
+  }
+
+  return {
+    banners,
+    push,
+    pushError,
+    dismiss,
+    clear,
+  }
+})