✨ tests: add binary e2e suite (Traefik binary + Go mock LAPI), run it in CI

Add a second e2e suite that runs Traefik as a downloaded binary with the
plugin loaded from source, and replaces Crowdsec with a small stdlib-only Go
LAPI mock driven via /admin endpoints. No Docker, no real Crowdsec.

The mock lives in its own nested Go module (tests/e2e/mock/mocklapi) so it
stays out of the plugin module's build, lint, test and vendor.

This suite validates the plugin's own behaviour (live/none/stream modes,
caching, trusted-IP bypass, ban/captcha rendering). Crowdsec and AppSec
correctness are out of scope on purpose — they are validated upstream by the
maintainer — so the AppSec scenario is intentionally absent and the README
says so to avoid misfiled issues.

CI now runs this suite only (`make e2e_mock`), since it needs neither Docker
nor a real Crowdsec. The Docker suite (tests/e2e/scenarios) is kept for local
debugging (`make e2e`).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/e2e/mock/scenarios/custom-ban-page/run.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+HERE="$(cd "$(dirname "$0")" && pwd)"
+# shellcheck source=../../lib/common.sh
+source "$HERE/../../lib/common.sh"
+
+SCENARIO=custom-ban-page
+
+body() {
+  echo "[$SCENARIO] adding ban decision"
+  lapi_add_decision 1.2.3.4 ban 5m
+
+  echo "[$SCENARIO] waiting one stream tick + buffer..."
+  sleep 4
+
+  echo "[$SCENARIO] banned response status is 403"
+  assert_status "http://127.0.0.1:${WEB_PORT}/foo" 403 -H "X-Forwarded-For: 1.2.3.4"
+
+  echo "[$SCENARIO] banned response Content-Type is HTML"
+  assert_header "http://127.0.0.1:${WEB_PORT}/foo" Content-Type "text/html; charset=utf-8" -H "X-Forwarded-For: 1.2.3.4"
+
+  echo "[$SCENARIO] banned response body contains the custom marker"
+  assert_body_contains "http://127.0.0.1:${WEB_PORT}/foo" "E2E_CUSTOM_BAN_PAGE_MARKER" -H "X-Forwarded-For: 1.2.3.4"
+}
+
+run_scenario "$SCENARIO" "$HERE" body