Add virtual-threads-benchmark-webflux: the WebFlux leg of the three-way benchmark

Fixes found during self-correction before publishing:
- /stream used Flux.interval(), which ticks on its own wall-clock schedule
  independent of downstream demand and threw OverflowException under a slow
  subscriber; switched to Flux.range(), which has no independent production
  schedule and can never outrun demand.
- Single-trial HTTP load tests on this shared sandbox swung by more than 50%
  run to run (795ms-1247ms observed on the identical /io endpoint back to
  back) -- large enough to flip which threading model looked faster. Fixed
  by taking the median of 5 independent trials for the I/O-bound benchmark
  and the median of 3 for the event-loop-starvation benchmark, rather than
  reporting a single noisy run as if it were precise.
- The event-loop-starvation test's first cut used only 8 concurrent /cpu
  requests as background load, which drained through the 4 event-loop
  threads well inside the /io measurement window and produced an
  inconsistent, sometimes-inverted result across runs; raising to 60 fixed
  the under-loading problem but still flaked once during verification
  (372ms vs 374ms p99, a real tie). Final fix: 150 concurrent requests plus
  the median-of-3 trials above.

Also adds StreamBackpressureTest, a StepVerifier proof that the /stream
endpoint never emits ahead of its subscriber's outstanding requests, and
updates the module's docs to report the de-noised numbers with an explicit
methodology note on how they compare to the single-trial platform/virtual-
thread numbers reused from a different post.

README.md

@@ -10,6 +10,8 @@ by that module's `scripts/run-all.sh`, never typed by hand.
 |---|---|---|
 | [`async/`](async/README.md) | [@Async in Spring Boot 4: Executors, Virtual Threads and the Self-Invocation Trap](https://ankurm.com/spring-boot-4-async-executors-virtual-threads/) | Which thread a method actually ran on, in every case where the answer is not the one you expect |
 | [`scheduling/`](scheduling/README.md) | [@Scheduled, ShedLock and Distributed Cron: Scheduling That Survives Three Replicas](https://ankurm.com/spring-scheduled-shedlock-distributed-cron/) | Three replicas against one database running the same job three times, then one row and one conditional UPDATE fixing it |
+| [`virtual-threads-benchmark/`](virtual-threads-benchmark/README.md) | [Virtual Threads on Spring Boot 4.1: The Benchmarks, Re-Run, and the Pinning Advice That Expired](https://ankurm.com/leveraging-virtual-threads-in-spring-boot-3-4-building-high-throughput-services/) | Platform threads vs virtual threads, re-benchmarked on Boot 4.1.1 / JDK 25, plus JEP 491's fix to `synchronized` pinning proven against a real JDK |
+| [`virtual-threads-benchmark-webflux/`](virtual-threads-benchmark-webflux/README.md) | [Virtual Threads vs Reactive (WebFlux) vs Platform Threads: Benchmarks and a Decision Framework](https://ankurm.com/virtual-threads-vs-webflux-vs-platform-threads-spring-boot-benchmarks/) | The WebFlux leg of the three-way comparison, plus the event-loop-starvation failure mode an isolated CPU benchmark can't show |
 
 ## Common ground
 
@@ -31,6 +33,13 @@ The `scheduling` module also needs a database. `scheduling/scripts/postgres.sh`
 throwaway PostgreSQL 14 into `target/` with no Docker and no root, which is how its transcripts
 were produced; `docker-compose.yml` is there for anyone who would rather use Docker.
 
+`virtual-threads-benchmark` and `virtual-threads-benchmark-webflux` are a similar pair: the
+first re-benchmarks platform threads against virtual threads for one post, the second adds the
+WebFlux leg for a different, three-way-comparison post, and reuses the first module's
+committed transcripts rather than re-measuring the same thing twice. Both use the same
+client-side load generator (`java.net.http.HttpClient` on a virtual-thread executor, client
+role only) so all three threading models in the three-way post are measured the same way.
+
 ## Licence
 
 MIT — see [LICENSE](LICENSE).