✨ tests: end-to-end suite scaffold + stream-mode scenario

Add tests/e2e/ structure with shared bash helpers and the first
scenario (stream-mode): spin up real Traefik + Crowdsec via docker
compose, mount the repo as a local plugin, add a ban via cscli, verify
the bouncer blocks the matching X-Forwarded-For, then delete the
decision and verify pass-through.

Adds .github/workflows/e2e.yml with one matrix job per scenario
(stream-mode for now), and Makefile targets `e2e` and `e2e_<scenario>`
for local runs.

Refs #328

tests/e2e/lib/common.sh

@@ -0,0 +1,78 @@
+#!/usr/bin/env bash
+# Shared helpers for end-to-end scenarios.
+# Dependencies: bash, curl, docker.
+
+# Wait until the Crowdsec LAPI reports ready, or fail after timeout.
+# Usage: wait_crowdsec_ready [container_name] [timeout_seconds]
+wait_crowdsec_ready() {
+  local container="${1:-crowdsec}"
+  local timeout="${2:-90}"
+  local elapsed=0
+  while (( elapsed < timeout )); do
+    if docker exec "$container" cscli lapi status >/dev/null 2>&1; then
+      return 0
+    fi
+    sleep 1
+    ((elapsed++))
+  done
+  echo "wait_crowdsec_ready: timed out after ${timeout}s waiting for $container" >&2
+  return 1
+}
+
+# Poll URL until it returns the expected status code, or fail.
+# Usage: wait_for_status URL CODE [TIMEOUT_SECONDS] [curl args...]
+wait_for_status() {
+  local url="$1" expected="$2" timeout="${3:-30}"
+  shift 3 || true
+  local elapsed=0
+  local got=""
+  while (( elapsed < timeout )); do
+    got=$(curl -s -o /dev/null -w '%{http_code}' "$@" "$url" || true)
+    if [[ "$got" == "$expected" ]]; then
+      return 0
+    fi
+    sleep 1
+    ((elapsed++))
+  done
+  echo "wait_for_status: $url expected $expected, last seen ${got:-<none>}" >&2
+  return 1
+}
+
+# Assert a single curl returns the expected status code.
+# Usage: assert_status URL CODE [curl args...]
+assert_status() {
+  local url="$1" expected="$2"
+  shift 2 || true
+  local got
+  got=$(curl -s -o /dev/null -w '%{http_code}' "$@" "$url")
+  if [[ "$got" != "$expected" ]]; then
+    echo "assert_status: $url expected $expected, got $got" >&2
+    return 1
+  fi
+}
+
+# Assert a response header matches a value (case-insensitive name).
+# Usage: assert_header URL HEADER VALUE [curl args...]
+assert_header() {
+  local url="$1" header="$2" expected="$3"
+  shift 3 || true
+  local got
+  got=$(curl -s -D - -o /dev/null "$@" "$url" | tr -d '\r' \
+    | awk -v h="${header,,}" -F': ' 'tolower($1) == h { print $2; exit }')
+  if [[ "$got" != "$expected" ]]; then
+    echo "assert_header: $url header $header expected \"$expected\", got \"$got\"" >&2
+    return 1
+  fi
+}
+
+# Dump diagnostic info for a compose project; called on failure.
+# Usage: dump_diagnostics PROJECT COMPOSE_FILE
+dump_diagnostics() {
+  local project="$1" compose_file="$2"
+  echo "=== docker compose ps ==="
+  docker compose -p "$project" -f "$compose_file" ps || true
+  echo "=== docker compose logs ==="
+  docker compose -p "$project" -f "$compose_file" logs --no-color || true
+  echo "=== cscli decisions list ==="
+  docker exec crowdsec cscli decisions list 2>/dev/null || true
+}