fix: add explicit return type and rename unused catch variable for ESLint

Author: yachikadev

apps/backend/src/routes/follow.ts

@@ -1,16 +1,18 @@
-import type { FastifyInstance, FastifyRequest, FastifyReply } from 'fastify';
+import { getPlatform, getProfileUrl, getWebViewUrl } from '@devcard/shared';
+
 import { decrypt } from '../utils/encryption.js';
 import { getErrorMessage } from '../utils/error.util.js';
-import { getPlatform, getProfileUrl, getWebViewUrl } from '@devcard/shared';
 import { followLogSchema } from '../validations/follow.validation.js';
+
 import type { AuthenticatedUser } from '../types/fastify.js';
+import type { FastifyInstance, FastifyRequest, FastifyReply } from 'fastify';
 
-export async function followRoutes(app: FastifyInstance) {
+export async function followRoutes(app: FastifyInstance): Promise<void> {
     app.addHook('preHandler', async (request, reply) => {
     const server = request.server;
     if (typeof server?.authenticate === 'function') { await server.authenticate(request, reply); return }
     if (typeof app.authenticate === 'function') { await app.authenticate(request, reply); return }
-    try { const payload = await request.jwtVerify<AuthenticatedUser>(); if (payload) request.user = payload; } catch (e) { reply.status(401).send({ error: 'Unauthorized' }) }
+    try { const payload = await request.jwtVerify<AuthenticatedUser>(); if (payload) {request.user = payload;} } catch (_e) { reply.status(401).send({ error: 'Unauthorized' }) }
   });
 
   // ─── Follow via API (Layer 1) ───