feat: add email notification system (Brevo SMTP + N8N daily digest)

- Add core notification service: types, email-service (nodemailer/Brevo SMTP), notification-service (digest builder, preference CRUD, HTML renderer)
- Add API routes: POST /api/notifications/digest (N8N cron, Bearer auth), GET/PUT /api/notifications/preferences (session auth)
- Add NotificationPreferences UI component (Bell button + dialog with per-type toggles) in Registratura toolbar
- Add 7 Brevo SMTP env vars to docker-compose.yml
- Update CLAUDE.md, ROADMAP.md, DATA-MODEL.md, SYSTEM-ARCHITECTURE.md, CONFIGURATION.md, DOCKER-DEPLOYMENT.md

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

docs/DATA-MODEL.md

@@ -443,6 +443,40 @@ interface WordTemplate extends BaseEntity {
 }
 ```
 
+### Email Notifications (platform service)
+
+```typescript
+// src/core/notifications/types.ts
+
+type NotificationType = "deadline-urgent" | "deadline-overdue" | "document-expiry";
+
+interface NotificationPreference {
+  userId: string;
+  email: string;
+  name: string;
+  company: CompanyId;
+  enabledTypes: NotificationType[];
+  globalOptOut: boolean;
+}
+
+interface DigestItem {
+  entryNumber: string;
+  subject: string;
+  label: string;
+  dueDate: string;        // YYYY-MM-DD
+  daysRemaining: number;  // negative = overdue
+  color: "red" | "yellow" | "blue";
+}
+
+interface DigestSection {
+  type: NotificationType;
+  title: string;
+  items: DigestItem[];
+}
+```
+
+> **Storage:** Preferences stored in `KeyValueStore` (namespace `notifications`, key `pref:<userId>`). No separate Prisma model needed.
+
 ---
 
 ## Naming Conventions