Serve hotlink images by single-segment access token URL.

Legacy GET /i/:uploadId/:secret unchanged. Lookup new uploads by access token hash; decrypt with token from path.

backend/src/main.ts

@@ -14,7 +14,10 @@ async function bootstrap() {
     const app = await NestFactory.create<NestExpressApplication>(AppModule, { bodyParser: false });
 
     app.setGlobalPrefix('api', {
-        exclude: [{ path: 'i/:id/:secret', method: RequestMethod.GET }]
+        exclude: [
+            { path: 'i/:id/:secret', method: RequestMethod.GET },
+            { path: 'i/:accessToken', method: RequestMethod.GET }
+        ]
     });
 
     const configService = app.get(ConfigService);