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/routes/adminArchives.js

@@ -9,6 +9,7 @@ const { requirePermission } = require('../middleware/permissions');
 const archiver = require('archiver');
 const StreamZip = require('node-stream-zip');
 const { requireEventOwnership } = require('../middleware/ownership');
+const { assertZipEntriesWithin } = require('../utils/safePath');
 const logger = require('../utils/logger');
 const { getPagination } = require('../utils/routeHelpers');
 const router = express.Router();
@@ -183,6 +184,16 @@ router.post('/:id/restore', adminAuth, requirePermission('archives.restore'), re
       const entries = Object.values(await zip.entries());
       logger.info(`Archive contains ${entries.length} entries`);
 
+      // Reject ZIP-slip entries before writing anything to disk — extract()
+      // does not neutralise `../` in entry names (GHSA-jfhw-fj23-fx6x).
+      try {
+        assertZipEntriesWithin(entries, eventDir);
+      } catch (slipErr) {
+        await zip.close();
+        logger.warn(`Refusing archive restore — unsafe entry path: ${slipErr.message}`);
+        return res.status(400).json({ error: 'Archive contains invalid entry paths' });
+      }
+
       // Stream-extract everything to disk
       await zip.extract(null, eventDir);
       await zip.close();