feat: Suchbegriff-Spalte + Filter-Chips im LeadVault

- GET /api/leads/search-terms: distinct Suchbegriffe aus DB
- Filter-Bar: Suchbegriff-Chips (amber), klickbar zum Filtern
- Tabelle: Suchbegriff-Spalte mit Chip — Klick filtert direkt
- Mehrere Suchbegriffe gleichzeitig filterbar (OR-Logik)

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

app/api/leads/route.ts

@@ -19,7 +19,7 @@ export async function GET(req: NextRequest) {
     const sourceTabs = searchParams.getAll("sourceTab");
     const priorities = searchParams.getAll("priority");
     const tags = searchParams.getAll("tags");
-    const searchTerm = searchParams.get("searchTerm") || "";
+    const searchTerms = searchParams.getAll("searchTerm");
 
     const where: Prisma.LeadWhereInput = {};
 
@@ -46,8 +46,8 @@ export async function GET(req: NextRequest) {
       if (capturedTo) where.capturedAt.lte = new Date(capturedTo);
     }
 
-    if (searchTerm) {
-      where.sourceTerm = { contains: searchTerm };
+    if (searchTerms.length > 0) {
+      where.sourceTerm = { in: searchTerms };
     }
 
     if (tags.length > 0) {