Security: Update @fastify/middie to fix CVE-2026-22031

## Vulnerability

**Package:** `@fastify/middie`  
**CVE:** CVE-2026-22031  
**Summary:** Fastify Middie Middleware Path Bypass  
**Advisory:** https://github.com/advisories/GHSA-cxrg-g7r8-w69p

## Current State

JSS currently depends on `@fastify/middie` version <=9.0.3 which is vulnerable.

## Fix

Update `@fastify/middie` to `^9.1.0` which contains the patch.