feat: LeadVault - zentrale Lead-Datenbank mit CRM-Funktionen

- Prisma-Schema: Lead + LeadEvent Modelle (Migration 20260320)
- lib/services/leadVault.ts: sinkLeadsToVault mit Deduplizierung
- Auto-Sync: alle 4 Pipelines schreiben Leads in LeadVault
- GET /api/leads: Filter, Sortierung, Pagination (Server-side)
- PATCH/DELETE /api/leads/[id]: Status, Priorität, Tags, Notizen
- POST /api/leads/bulk: Bulk-Aktionen für mehrere Leads
- GET /api/leads/stats: Statistiken + 7-Tage-Sparkline
- POST /api/leads/quick-serp: SERP-Capture ohne Enrichment
- GET /api/leads/export: CSV-Export mit allen Feldern
- app/leadvault/page.tsx: vollständige UI mit Stats, Quick SERP,
  Filter-Leiste, sortierbare Tabelle, Bulk-Aktionen, Side Panel
- Sidebar: LeadVault-Eintrag mit Live-Badge (neue Leads)

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

prisma/schema.prisma

@@ -41,3 +41,57 @@ model LeadResult {
   source       String?
   createdAt    DateTime @default(now())
 }
+
+model Lead {
+  id              String    @id @default(cuid())
+
+  domain          String?
+  companyName     String?
+  contactName     String?
+  contactTitle    String?
+  email           String?
+  linkedinUrl     String?
+  phone           String?
+
+  sourceTab       String
+  sourceTerm      String?
+  sourceJobId     String?
+
+  serpTitle       String?
+  serpSnippet     String?
+  serpRank        Int?
+  serpUrl         String?
+
+  emailConfidence Float?
+
+  status          String    @default("new")
+  priority        String    @default("normal")
+  notes           String?
+
+  tags            String?
+  country         String?
+  headcount       String?
+  industry        String?
+
+  capturedAt      DateTime  @default(now())
+  contactedAt     DateTime?
+  updatedAt       DateTime  @updatedAt
+
+  events          LeadEvent[]
+
+  @@index([domain])
+  @@index([status])
+  @@index([sourceTab])
+  @@index([capturedAt])
+  @@index([email])
+}
+
+model LeadEvent {
+  id      String   @id @default(cuid())
+  leadId  String
+  lead    Lead     @relation(fields: [leadId], references: [id], onDelete: Cascade)
+  event   String
+  at      DateTime @default(now())
+
+  @@index([leadId])
+}