Upgrade Apollo Server 4 to 5

@apollo/server v4 reached end-of-life on January 26, 2026. This bumps
to v5 (resolves to 5.5.0) and raises the graphql peer requirement to
^16.11.0 as required by AS5. No application code changes were needed
since the project already used the AS5-compatible patterns (separate
@as-integrations/express5 package, context in expressMiddleware options).

https://claude.ai/code/session_015DcGUmHQtHQRt2QUSefXga

package.json

@@ -26,12 +26,12 @@
   },
   "private": true,
   "dependencies": {
-    "@apollo/server": "^4.11.2",
+    "@apollo/server": "^5.0.0",
     "@as-integrations/express5": "^1.1.2",
     "express": "^5.1.0",
     "express-rate-limit": "^8.0.1",
     "express-slow-down": "^3.0.0",
-    "graphql": "^16.10.0",
+    "graphql": "^16.11.0",
     "jsonwebtoken": "^9.0.2",
     "redis": "^4.7.0"
   },