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/layout/AppShell.tsx

@@ -39,6 +39,8 @@ import { UserMenu } from './UserMenu'
 import { NotificationButton } from './NotificationButton'
 import { RightContextPanel } from './RightContextPanel'
 import { CompareTray } from './CompareTray'
+import { GlobalAIAssistantDrawer, GlobalAIAssistantButton } from '../assistant'
+import { useAssistantStore } from '../../stores/assistantStore'
 
 // ---------------------------------------------------------------------------
 // Types
@@ -435,6 +437,7 @@ interface TopBarProps {
 function TopBar({ activeWorkspace, pathname }: TopBarProps) {
   const config = WORKSPACE_CONFIG[activeWorkspace]
   const pageName = getPageNameFromPath(pathname)
+  const openAssistant = useAssistantStore(s => s.open)
 
   return (
     <Box
@@ -478,6 +481,7 @@ function TopBar({ activeWorkspace, pathname }: TopBarProps) {
           variant="outlined"
           size="small"
           startIcon={<Sparkles size={14} />}
+          onClick={openAssistant}
           sx={{ textTransform: 'none', fontSize: '0.8125rem' }}
         >
           AI Assistent
@@ -540,6 +544,8 @@ export function AppShell() {
       </Box>
 
       <CompareTray />
+      <GlobalAIAssistantDrawer />
+      <GlobalAIAssistantButton />
     </Box>
   )
 }