docs: fix review findings in README/ROADMAP

- Correct net/http interop claim: Echo handlers are not http.Handler;
  interop is via WrapHandler/WrapMiddleware
- Clarify binding ships with a pluggable validator (not built-in validation)
- ROADMAP: reference canonical auto-HEAD issue/PR (#2895/#2949) instead of
  the duplicate PRs (#2944/#2937) slated for closure

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: vishr

README.md

@@ -13,7 +13,7 @@
 
 High performance, extensible, minimalist Go web framework.
 
-Echo is built on Go's standard `net/http` — handlers stay `http.Handler`-compatible — and adds the parts the standard library leaves to you: a fast radix-tree router, request binding and validation, a deep middleware ecosystem, and centralized error handling. Actively maintained, with `v5` as the current release line (see badges above for the latest version and most recent commit).
+Echo is built on Go's standard `net/http` — and interoperates with it via `echo.WrapHandler` / `echo.WrapMiddleware` — adding the parts the standard library leaves to you: a fast radix-tree router, request binding (with a pluggable validator), a deep middleware ecosystem, and centralized error handling. Actively maintained, with `v5` as the current release line (see badges above for the latest version and most recent commit).
 
 * [Official website](https://echo.labstack.com)
 * [Quick start](https://echo.labstack.com/docs/quick-start)

ROADMAP.md

@@ -30,7 +30,7 @@ Echo supports the **latest four Go major releases** and may work with older vers
 These are frequently-requested items being discussed. Inclusion here is **not** a
 commitment — each still needs design agreement before implementation:
 
-- **Automatic `HEAD` for `GET` routes** (#2944, #2937) — opt-in, likely via an
+- **Automatic `HEAD` for `GET` routes** (#2895; see #2949) — opt-in, likely via an
   `OnAddRoute` hook so users keep control.
 - **Rate limiter response metadata** — expose `Retry-After` / remaining quota
   through the store interface (#2961).