feat(rack-planner): implement port-to-port connections (patch cables) with dynamic SVG visualization layer

server/services/connectionService.ts

@@ -0,0 +1,34 @@
+import { prisma } from '../lib/prisma';
+import { AppError } from '../types/index';
+
+export async function createConnection(data: { fromPortId: string; toPortId: string; color?: string; label?: string }) {
+  // Check if both ports exist
+  const [from, to] = await Promise.all([
+    prisma.port.findUnique({ where: { id: data.fromPortId } }),
+    prisma.port.findUnique({ where: { id: data.toPortId } }),
+  ]);
+
+  if (!from || !to) throw new AppError('One or both ports not found', 404, 'NOT_FOUND');
+  if (from.id === to.id) throw new AppError('Cannot connect a port to itself', 400, 'BAD_REQUEST');
+
+  // Check if ports are already occupied? 
+  // (In real life, a port can only have one cable, but we might allow one source and one target per port if we want to be flexible, but better to prevent simple loops)
+  
+  // Create connection (if it already exists, use upsert or just throw error; @@unique already handles it)
+  return prisma.connection.create({ data });
+}
+
+export async function deleteConnection(id: string) {
+  return prisma.connection.delete({ where: { id } });
+}
+
+export async function deleteByPorts(portId1: string, portId2: string) {
+  return prisma.connection.deleteMany({
+    where: {
+      OR: [
+        { fromPortId: portId1, toPortId: portId2 },
+        { fromPortId: portId2, toPortId: portId1 },
+      ],
+    },
+  });
+}