echo-guard cannot be used with Echo v5 #51

echo-guard only supports Echo v4. Echo v5 changes the public types (echo.Context is now a struct taken as *echo.Context, c.Response() returns an http.ResponseWriter, c.Error is gone), so v1.x cannot be used from an Echo v5 app.

knadh/listmonk moved to github.com/labstack/echo/v5 v5.4.0 on 2026-10-18 (its commit 52f80ccc), so the integration proposed in knadh/listmonk#3282 needs Echo v5 support.

Plan:

1. master becomes the Echo v5 line as module github.com/rennf93/echo-guard/v2. Go's semantic import versioning requires the /v2 path because New, GuardWebSocket, NewStatusHandler and AddStatusRoute change signature.
2. Echo v4 users stay on v1.x. Branch v1 keeps the v1.5.0 code for fixes.
3. Same behavior contract: exact verdict translation, fail-closed 500, bounded body replay, route identity from the request context, RemoteAddr as the only client host.
4. The engine floor rises to guard-core-go v4.4.1, which stops printing the spec DEBUG lines on every request.