feat: frontend AI tab — KI-Strategie, KI-Entwurf, Aehnliche Faelle

New "KI" tab on case detail page with three sub-panels:
- KI-Strategie: one-click strategic analysis with next steps, risks, timeline
- KI-Entwurf: document drafting with template selection, language, instructions
- Aehnliche Faelle: UPC similar case search with relevance scores

Components: CaseStrategy, DocumentDrafter, SimilarCaseFinder
Types: StrategyRecommendation, DocumentDraft, SimilarCase, etc.

frontend/src/app/(app)/cases/[id]/layout.tsx

@@ -17,6 +17,7 @@ import {
   StickyNote,
   AlertTriangle,
   ScrollText,
+  Brain,
 } from "lucide-react";
 import { format } from "date-fns";
 import { de } from "date-fns/locale";
@@ -48,6 +49,7 @@ const TABS = [
   { segment: "mitarbeiter", label: "Mitarbeiter", icon: UserCheck },
   { segment: "notizen", label: "Notizen", icon: StickyNote },
   { segment: "protokoll", label: "Protokoll", icon: ScrollText },
+  { segment: "ki", label: "KI", icon: Brain },
 ] as const;
 
 const TAB_LABELS: Record<string, string> = {
@@ -58,6 +60,7 @@ const TAB_LABELS: Record<string, string> = {
   mitarbeiter: "Mitarbeiter",
   notizen: "Notizen",
   protokoll: "Protokoll",
+  ki: "KI",
 };
 
 function CaseDetailSkeleton() {