Add series fields to audiobooks and update related logic

Introduces 'series' and 'seriesPart' fields to the Audiobook model and database schema. Updates API routes, file organization, and path template utilities to support series metadata. Enhances chapter merging logic, improves notification backend testing, and expands test coverage for admin and API routes.

src/app/api/admin/notifications/test/route.ts

@@ -8,12 +8,29 @@ import { requireAuth, requireAdmin, AuthenticatedRequest } from '@/lib/middlewar
 import { getNotificationService, NotificationBackendType, NotificationPayload } from '@/lib/services/notification.service';
 import { RMABLogger } from '@/lib/utils/logger';
 import { z } from 'zod';
+import { prisma } from '@/lib/db';
 
 const logger = RMABLogger.create('API.Admin.Notifications.Test');
 
-const TestNotificationSchema = z.object({
-  type: z.enum(['discord', 'pushover', 'email', 'slack', 'telegram', 'webhook']),
-  config: z.record(z.any()),
+const TestNotificationSchema = z.discriminatedUnion('mode', [
+  // Test existing backend by ID (uses stored config)
+  z.object({
+    mode: z.literal('backend'),
+    backendId: z.string(),
+  }),
+  // Test new config before saving
+  z.object({
+    mode: z.literal('config'),
+    type: z.enum(['discord', 'pushover', 'email', 'slack', 'telegram', 'webhook']),
+    config: z.record(z.any()),
+  }),
+]);
+
+// Support legacy format without mode
+const LegacyTestNotificationSchema = z.object({
+  backendId: z.string().optional(),
+  type: z.enum(['discord', 'pushover', 'email', 'slack', 'telegram', 'webhook']).optional(),
+  config: z.record(z.any()).optional(),
 });
 
 /**
@@ -25,12 +42,67 @@ export async function POST(request: NextRequest) {
     return requireAdmin(req, async () => {
       try {
         const body = await request.json();
-        const { type, config } = TestNotificationSchema.parse(body);
+
+        // Support legacy format for backward compatibility
+        const legacyParsed = LegacyTestNotificationSchema.safeParse(body);
+
+        let type: NotificationBackendType;
+        let encryptedConfig: any;
 
         const notificationService = getNotificationService();
 
-        // Encrypt config values
-        const encryptedConfig = notificationService.encryptConfig(type, config);
+        if (legacyParsed.success) {
+          // Legacy format
+          if (legacyParsed.data.backendId) {
+            // Test existing backend
+            const backend = await prisma.notificationBackend.findUnique({
+              where: { id: legacyParsed.data.backendId },
+            });
+
+            if (!backend) {
+              return NextResponse.json(
+                { error: 'NotFound', message: 'Backend not found' },
+                { status: 404 }
+              );
+            }
+
+            type = backend.type as NotificationBackendType;
+            encryptedConfig = backend.config; // Already encrypted in DB
+          } else if (legacyParsed.data.type && legacyParsed.data.config) {
+            // Test new config
+            type = legacyParsed.data.type as NotificationBackendType;
+            encryptedConfig = notificationService.encryptConfig(type, legacyParsed.data.config);
+          } else {
+            return NextResponse.json(
+              { error: 'ValidationError', message: 'Must provide either backendId or type+config' },
+              { status: 400 }
+            );
+          }
+        } else {
+          // New format with discriminated union
+          const parsed = TestNotificationSchema.parse(body);
+
+          if (parsed.mode === 'backend') {
+            // Test existing backend
+            const backend = await prisma.notificationBackend.findUnique({
+              where: { id: parsed.backendId },
+            });
+
+            if (!backend) {
+              return NextResponse.json(
+                { error: 'NotFound', message: 'Backend not found' },
+                { status: 404 }
+              );
+            }
+
+            type = backend.type as NotificationBackendType;
+            encryptedConfig = backend.config; // Already encrypted in DB
+          } else {
+            // Test new config
+            type = parsed.type;
+            encryptedConfig = notificationService.encryptConfig(type, parsed.config);
+          }
+        }
 
         // Create test payload
         const testPayload: NotificationPayload = {