fix(server): raise express.json body limit to 10mb

Express defaults to a 100kb JSON body, which is too small for realistic
imports through POST /api/v1/monitors/import/json (backups with many
monitors and their config easily exceed 100kb, returning
"request entity too large").

Raise the parser cap to 10mb. That covers real-world import payloads
while keeping the DoS surface bounded — a larger, streaming file-upload
route for imports remains desirable as a follow-up.

server/src/app.ts

@@ -54,7 +54,7 @@ export const createApp = ({
 
 	app.use(express.static(frontendPath));
 
-	app.use(express.json());
+	app.use(express.json({ limit: "10mb" }));
 	app.use(cookieParser());
 
 	app.use(sanitizeBody());