feat: F024 global AI assistant — contextual decision intelligence drawer

Wires the existing "AI Assistent" button in the TopBar and adds a 420px
slide-in drawer with context-aware suggestions, message thread, loading
animation, and action cards requiring manual confirmation. Template-based
mock service returns German-language answers keyed by route + question
keywords — no real LLM calls, no invented facts.

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

src/stores/assistantStore.ts

@@ -0,0 +1,36 @@
+import { create } from 'zustand'
+import type { AssistantContext, AssistantMessage } from '../domain/assistant'
+
+interface AssistantState {
+  isOpen: boolean
+  context: AssistantContext | null
+  messages: AssistantMessage[]
+  isLoading: boolean
+  error: string | null
+
+  open: () => void
+  close: () => void
+  setContext: (ctx: AssistantContext) => void
+  updateContext: (partial: Partial<AssistantContext>) => void
+  addMessage: (msg: AssistantMessage) => void
+  setLoading: (v: boolean) => void
+  setError: (e: string | null) => void
+  clearConversation: () => void
+}
+
+export const useAssistantStore = create<AssistantState>((set) => ({
+  isOpen: false,
+  context: null,
+  messages: [],
+  isLoading: false,
+  error: null,
+
+  open: () => set({ isOpen: true }),
+  close: () => set({ isOpen: false }),
+  setContext: (ctx) => set({ context: ctx }),
+  updateContext: (partial) => set((s) => ({ context: s.context ? { ...s.context, ...partial } : null })),
+  addMessage: (msg) => set((s) => ({ messages: [...s.messages, msg] })),
+  setLoading: (v) => set({ isLoading: v }),
+  setError: (e) => set({ error: e }),
+  clearConversation: () => set({ messages: [], error: null }),
+}))