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>

app/api/geofences/[id]/route.ts

@@ -0,0 +1,64 @@
+import { NextResponse } from "next/server";
+import { auth } from "@/lib/auth";
+import { geofenceDb } from "@/lib/geofence-db";
+
+// DELETE /api/geofences/[id] - Delete a geofence
+export async function DELETE(
+  request: Request,
+  { params }: { params: Promise<{ id: string }> }
+) {
+  try {
+    const session = await auth();
+
+    if (!session?.user) {
+      return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+    }
+
+    const userId = (session.user as any).id;
+    const { id: geofenceId } = await params;
+
+    // Check if geofence exists
+    const geofence = geofenceDb.findById(geofenceId);
+
+    if (!geofence) {
+      return NextResponse.json(
+        { error: "Geofence not found" },
+        { status: 404 }
+      );
+    }
+
+    // Check ownership
+    if (geofence.owner_id !== userId) {
+      return NextResponse.json(
+        { error: "Forbidden: You can only delete your own geofences" },
+        { status: 403 }
+      );
+    }
+
+    // Delete geofence (CASCADE will delete related events and status)
+    const deleted = geofenceDb.delete(geofenceId);
+
+    if (!deleted) {
+      return NextResponse.json(
+        { error: "Failed to delete geofence" },
+        { status: 500 }
+      );
+    }
+
+    console.log(`[DELETE /api/geofences/${geofenceId}] Deleted geofence ${geofence.name} for user ${userId}`);
+
+    return NextResponse.json({
+      success: true,
+      message: "Geofence deleted successfully",
+    });
+  } catch (error) {
+    console.error(`[DELETE /api/geofences/[id]] Error:`, error);
+    return NextResponse.json(
+      {
+        error: "Failed to delete geofence",
+        details: error instanceof Error ? error.message : "Unknown error",
+      },
+      { status: 500 }
+    );
+  }
+}