Implement outbound LAN gateway

Add fips-gateway binary: a separate daemon that allows unmodified LAN
hosts to reach FIPS mesh destinations via DNS-allocated virtual IPs
and kernel nftables NAT.

Gateway DNS resolver: forwarding proxy on [::]:53 that intercepts
.fips queries, forwards to daemon resolver (localhost:5354), allocates
virtual IPs from pool, returns AAAA records. Always sends AAAA upstream
regardless of client query type, returns proper NODATA for non-AAAA.

Virtual IP pool: fd01::/112 pool with state machine lifecycle
(Allocated → Active → Draining → Free), TTL-based reclamation,
conntrack integration for session tracking.

NAT manager: nftables DNAT/SNAT rules via rustables netlink API,
per-mapping rule lifecycle, fips0 masquerade for LAN client source
address rewriting.

Network setup: local pool route, proxy NDP for virtual IPs on LAN
interface, IPv6 forwarding validation.

Control socket at /run/fips/gateway.sock with show_gateway and
show_mappings queries. fipstop Gateway tab with pool summary gauge
and mappings table.

Gateway config section in fips.yaml with pool CIDR, LAN interface,
DNS upstream, TTL, and grace period settings.

Design doc at docs/design/fips-gateway.md.

Integration test (testing/static/scripts/gateway-test.sh): three
containers verifying DNS resolution, end-to-end HTTP, NAT state,
TTL expiration, SERVFAIL fallback, and clean shutdown.

testing/ci-local.sh

@@ -14,7 +14,7 @@
 #   -h, --help           Show this help
 #
 # Integration suites:
-#   static-mesh, static-chain, rekey,
+#   static-mesh, static-chain, rekey, gateway,
 #   chaos-smoke-10, chaos-churn-mixed-10, chaos-ethernet-mesh,
 #   chaos-ethernet-only, chaos-tcp-mesh, chaos-bottleneck-parent,
 #   chaos-cost-avoidance, chaos-cost-reeval, chaos-cost-stability,
@@ -63,6 +63,7 @@ CHAOS_SUITES=(
     "mixed-technology mixed-technology"
     "congestion-stress congestion-stress"
 )
+GATEWAY_SUITES=(gateway)
 SIDECAR_SUITES=(sidecar)
 
 # ── Colors ─────────────────────────────────────────────────────────────────
@@ -98,6 +99,9 @@ list_suites() {
         echo "    chaos-${parts[0]}  (${parts[*]:1})"
     done
     echo ""
+    echo "  Gateway:"
+    for s in "${GATEWAY_SUITES[@]}"; do echo "    $s"; done
+    echo ""
     echo "  Sidecar:"
     for s in "${SIDECAR_SUITES[@]}"; do echo "    $s"; done
     exit 0
@@ -195,8 +199,10 @@ install_binaries() {
     cp target/release/fips "$dest/fips"
     cp target/release/fipsctl "$dest/fipsctl"
     [[ -f target/release/fipstop ]] && cp target/release/fipstop "$dest/fipstop" || true
+    [[ -f target/release/fips-gateway ]] && cp target/release/fips-gateway "$dest/fips-gateway" || true
     chmod +x "$dest/fips" "$dest/fipsctl"
     [[ -f "$dest/fipstop" ]] && chmod +x "$dest/fipstop" || true
+    [[ -f "$dest/fips-gateway" ]] && chmod +x "$dest/fips-gateway" || true
 }
 
 # Run a static topology test (mesh, chain)
@@ -265,6 +271,31 @@ run_chaos() {
     record "chaos-$name" $rc
 }
 
+# Run gateway integration test
+run_gateway() {
+    local compose="testing/static/docker-compose.yml"
+    local rc=0
+
+    info "[gateway] Generating configs"
+    bash testing/static/scripts/generate-configs.sh gateway gateway-test || { record "gateway" 1; return; }
+    bash testing/static/scripts/gateway-test.sh inject-config || { record "gateway" 1; return; }
+
+    info "[gateway] Starting containers"
+    docker compose -f "$compose" --profile gateway up -d || { record "gateway" 1; return; }
+
+    info "[gateway] Running gateway test"
+    if bash testing/static/scripts/gateway-test.sh; then
+        rc=0
+    else
+        rc=1
+        info "[gateway] Collecting failure logs"
+        docker compose -f "$compose" --profile gateway logs --no-color 2>&1 | tail -100
+    fi
+
+    docker compose -f "$compose" --profile gateway down --volumes --remove-orphans 2>/dev/null
+    record "gateway" $rc
+}
+
 # Run sidecar test
 run_sidecar() {
     local rc=0
@@ -307,6 +338,9 @@ run_integration() {
     # Rekey
     run_rekey
 
+    # Gateway
+    run_gateway
+
     # Chaos scenarios (parallel, throttled)
     if [[ "$SKIP_CHAOS" != true ]]; then
         info "Running ${#CHAOS_SUITES[@]} chaos scenarios (max $PARALLEL_JOBS parallel)"
@@ -369,6 +403,8 @@ run_suite() {
             run_static "${suite#static-}" ;;
         rekey)
             run_rekey ;;
+        gateway)
+            run_gateway ;;
         chaos-*)
             local chaos_name="${suite#chaos-}"
             local found=false