Add session revocation & consolidate rate limiting

Add sessions_invalidated_at to users (migration + Prisma schema) to support immediate session revocation. Set sessionsInvalidatedAt when an admin revokes a user's login token and enforce revocation checks in auth middleware and the refresh endpoint (compare token iat against sessionsInvalidatedAt). Add optional iat fields to JWT payload types. Scrub token from browser history after token-login. Consolidate rate-limiting logic into src/lib/utils/rateLimit.ts (rename/merge previous auth/apiToken rate limiter implementations), remove the old apiTokenRateLimit.ts, and update imports and tests to use the new module.

src/app/api/admin/users/[id]/login-token/route.ts

@@ -79,7 +79,7 @@ export async function DELETE(
 
         await prisma.user.update({
           where: { id },
-          data: { loginTokenHash: null },
+          data: { loginTokenHash: null, sessionsInvalidatedAt: new Date() },
         });
 
         logger.info('Admin revoked login token for user', {