fix(security): reject ZIP-slip entries in archive/backup restore (GHSA-jfhw-fj23-fx6x)

node-stream-zip's extract(null, root) writes each entry to path.join(root,
entry.name) without neutralising '../', so a crafted archive entry named
'../../uploads/logos/evil.svg' escaped the target dir and overwrote arbitrary
files (logos, .env, route files → RCE on source deploys). Requires admin with
archives.restore.

Adds assertZipEntriesWithin() to utils/safePath.js — a lexical containment
check run on the entry list BEFORE extract() — and guards both extract sinks:
adminArchives.js (the reported route) and picpeakImportService.js (the sibling
.picpeak import, same sink). Adds unit tests for traversal, absolute-path, and
sibling-prefix entries.

backend/src/services/picpeakImportService.js

@@ -18,6 +18,7 @@ const fsp = require('fs').promises;
 const path = require('path');
 const os = require('os');
 const StreamZip = require('node-stream-zip');
+const { assertZipEntriesWithin } = require('../utils/safePath');
 const { db } = require('../database/db');
 const knexConfig = require('../../knexfile');
 const { getStoragePath } = require('../config/storage');
@@ -232,6 +233,10 @@ async function importFromPicpeak({ picpeakPath, currentAdminId }) {
   try {
     const zip = new StreamZip.async({ file: picpeakPath });
     try {
+      // Reject ZIP-slip entries before extracting — a crafted .picpeak could
+      // otherwise write outside the staging dir via `../` entry names
+      // (same class as GHSA-jfhw-fj23-fx6x).
+      assertZipEntriesWithin(Object.values(await zip.entries()), staging);
       await zip.extract(null, staging);
     } finally {
       await zip.close();