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/components/assistant/index.ts

@@ -0,0 +1,8 @@
+export { GlobalAIAssistantButton } from './GlobalAIAssistantButton'
+export { GlobalAIAssistantDrawer } from './GlobalAIAssistantDrawer'
+export { AssistantMessageList } from './AssistantMessageList'
+export { AssistantPromptSuggestions } from './AssistantPromptSuggestions'
+export { AssistantContextSummary } from './AssistantContextSummary'
+export { AssistantActionCards } from './AssistantActionCards'
+export { AssistantLoadingState } from './AssistantLoadingState'
+export { AssistantErrorState } from './AssistantErrorState'