Add FRR anycast lab: HLD, containerized topology, docs

Реализует HLD-дизайн (hld.md) в виде развёртываемого Docker Compose
окружения: 5 FRR-роутеров (A1-A3 anycast 10.200.200.1/32 на AS 65001,
B1/B2 на AS 65002/65003) + 6 клиентских контейнеров, ECMP-балансировка
трафика клиентов площадки B к anycast-адресу площадки A.

- docker-compose.yml, frr/*, entrypoints/* — топология и конфиги FRR
- scripts/verify.sh, scripts/traffic-test.sh — проверка BGP/ECMP и трафика
- hld.md — HLD-дизайн + Mermaid-диаграмма топологии
- README.md — запуск, структура, команды проверки на роутерах и клиентах
- docs/ — планы внедрения и summary по каждому изменению

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bc3HkMiDwooSyLBLoMKNyF

scripts/traffic-test.sh

@@ -0,0 +1,32 @@
+#!/bin/sh
+# Drives traffic from a Site-B client to the anycast address and shows which
+# A-node (a1/a2/a3) answered each request, demonstrating ECMP distribution.
+# Usage: scripts/traffic-test.sh [client] [request-count]
+set -e
+cd "$(dirname "$0")/.."
+
+CLIENT="${1:-c1}"
+COUNT="${2:-20}"
+DST="10.200.200.1"
+
+echo "==== $CLIENT: ping $DST ===="
+docker compose exec -T "$CLIENT" ping -c 4 "$DST"
+
+echo
+echo "==== $CLIENT: traceroute $DST ===="
+docker compose exec -T "$CLIENT" traceroute -n -m 5 "$DST" 2>&1 || true
+
+echo
+echo "==== $CLIENT: $COUNT requests to http://$DST, varying source port (ECMP hash input) ===="
+RESULTS=$(docker compose exec -T "$CLIENT" sh -c '
+  for i in $(seq 1 '"$COUNT"'); do
+    port=$((30000 + i))
+    node=$(curl -s --local-port "$port" --max-time 3 "http://'"$DST"'/" || echo "no-answer")
+    echo "req $i (src-port $port) -> $node"
+  done
+')
+echo "$RESULTS"
+
+echo
+echo "Distribution:"
+echo "$RESULTS" | awk '{print $NF}' | sort | uniq -c

scripts/verify.sh

@@ -0,0 +1,16 @@
+#!/bin/sh
+# Checks that BGP has converged and that b1/b2 have 3-way ECMP to the anycast prefix.
+set -e
+cd "$(dirname "$0")/.."
+
+for n in a1 a2 a3 b1 b2; do
+  echo "==== $n: show bgp summary ===="
+  docker compose exec -T "$n" vtysh -c "show bgp summary"
+  echo
+done
+
+for n in b1 b2; do
+  echo "==== $n: show ip route 10.200.200.1/32 ===="
+  docker compose exec -T "$n" vtysh -c "show ip route 10.200.200.1/32"
+  echo
+done