chore: hoist token.sessionVersion ?? 0 into a named local

Slightly easier to read the cross-check condition when the JWT-side
value isn't sharing a line with the && and the inequality. No behavior
change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: msukkari

packages/web/src/auth.ts

@@ -303,7 +303,8 @@ const nextAuthResult = NextAuth({
                 // invalidated since the JWT was minted. Returning null here
                 // is what makes invalidation visible at /api/auth/session,
                 // not just at withAuth-gated endpoints.
-                if (!user && (token.sessionVersion ?? 0) !== dbUser.sessionVersion) {
+                const tokenSessionVersion = token.sessionVersion ?? 0;
+                if (!user && tokenSessionVersion !== dbUser.sessionVersion) {
                     return null;
                 }