Add Geofence MVP feature implementation

Implemented complete MVP for geofencing functionality with database,
backend logic, MQTT integration, and API endpoints.

**Phase 1: Database & Core Logic**
- scripts/init-geofence-db.js: Database initialization for Geofence tables
- lib/types.ts: TypeScript types for Geofence, GeofenceEvent, GeofenceStatus
- lib/geofence-engine.ts: Core geofencing logic (Haversine distance, state tracking)
- lib/geofence-db.ts: Database layer with CRUD operations
- package.json: Added db:init:geofence script

**Phase 2: MQTT Integration & Email Notifications**
- emails/geofence-enter.tsx: React Email template for enter events
- emails/geofence-exit.tsx: React Email template for exit events
- lib/email-renderer.ts: Added geofence email rendering functions
- lib/geofence-notifications.ts: Notification service for geofence events
- lib/mqtt-subscriber.ts: Integrated automatic geofence checking on location updates

**Phase 3: Minimal API**
- app/api/geofences/route.ts: GET (list) and POST (create) endpoints
- app/api/geofences/[id]/route.ts: DELETE endpoint
- All endpoints with authentication and ownership checks

**MVP Simplifications:**
- No zone limit enforcement (unlimited for all users)
- No notification flags (always send Enter + Exit emails)
- Device assignment required (no NULL device logic)
- Circular geofences only

**Features:**
✅ Automatic geofence detection on MQTT location updates
✅ Email notifications for enter/exit events
✅ State tracking to prevent duplicate events
✅ REST API for geofence management
✅ Non-blocking async processing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

emails/geofence-exit.tsx

@@ -0,0 +1,134 @@
+import { Link, Section, Text } from '@react-email/components';
+import * as React from 'react';
+import { EmailLayout } from './components/email-layout';
+import { EmailHeader } from './components/email-header';
+import { EmailFooter } from './components/email-footer';
+
+interface GeofenceExitEmailProps {
+  username: string;
+  deviceName: string;
+  geofenceName: string;
+  timestamp: string;
+  latitude: number | string;
+  longitude: number | string;
+  distanceFromCenter: number;
+  mapUrl?: string;
+}
+
+export const GeofenceExitEmail = ({
+  username = 'User',
+  deviceName = 'Device',
+  geofenceName = 'Zone',
+  timestamp = new Date().toISOString(),
+  latitude = 0,
+  longitude = 0,
+  distanceFromCenter = 0,
+  mapUrl,
+}: GeofenceExitEmailProps) => {
+  const formattedTimestamp = new Date(timestamp).toLocaleString('de-DE', {
+    dateStyle: 'long',
+    timeStyle: 'short',
+  });
+
+  const formattedDistance = Math.round(distanceFromCenter);
+
+  return (
+    <EmailLayout preview={`${deviceName} hat ${geofenceName} verlassen`}>
+      <EmailHeader title="Geofence Benachrichtigung" />
+
+      <Section style={content}>
+        <Text style={paragraph}>Hallo {username},</Text>
+
+        <Text style={paragraphBold}>
+          Ihr Gerät "{deviceName}" hat die Zone "{geofenceName}" verlassen.
+        </Text>
+
+        <Section style={detailsBox}>
+          <Text style={detailsTitle}>Details:</Text>
+          <Text style={detailItem}>
+            <strong>Zeit:</strong> {formattedTimestamp}
+          </Text>
+          <Text style={detailItem}>
+            <strong>Position:</strong> {latitude}, {longitude}
+          </Text>
+          <Text style={detailItem}>
+            <strong>Distanz vom Zentrum:</strong> {formattedDistance} Meter
+          </Text>
+        </Section>
+
+        {mapUrl && (
+          <Text style={paragraph}>
+            <Link href={mapUrl} style={link}>
+              → Position auf Karte anzeigen
+            </Link>
+          </Text>
+        )}
+
+        <Text style={footerText}>
+          Diese Benachrichtigung wurde automatisch von Ihrem Location Tracker System gesendet.
+        </Text>
+      </Section>
+
+      <EmailFooter />
+    </EmailLayout>
+  );
+};
+
+export default GeofenceExitEmail;
+
+const content = {
+  padding: '20px 40px',
+};
+
+const paragraph = {
+  color: '#374151',
+  fontSize: '16px',
+  lineHeight: '1.6',
+  margin: '0 0 16px',
+};
+
+const paragraphBold = {
+  ...paragraph,
+  fontSize: '18px',
+  fontWeight: '600',
+  color: '#dc2626', // Red for exit event
+};
+
+const detailsBox = {
+  backgroundColor: '#f9fafb',
+  border: '1px solid #e5e7eb',
+  borderRadius: '8px',
+  padding: '16px',
+  margin: '20px 0',
+};
+
+const detailsTitle = {
+  color: '#111827',
+  fontSize: '14px',
+  fontWeight: '600',
+  margin: '0 0 12px',
+  textTransform: 'uppercase' as const,
+  letterSpacing: '0.5px',
+};
+
+const detailItem = {
+  color: '#374151',
+  fontSize: '15px',
+  lineHeight: '1.6',
+  margin: '0 0 8px',
+};
+
+const link = {
+  color: '#2563eb',
+  textDecoration: 'underline',
+  fontSize: '16px',
+};
+
+const footerText = {
+  color: '#6b7280',
+  fontSize: '14px',
+  lineHeight: '1.5',
+  margin: '24px 0 0',
+  paddingTop: '16px',
+  borderTop: '1px solid #e5e7eb',
+};