fix(remote_ip): log IPv6 in canonical hex via :inet.ntoa

IPv6 segments were being printed in decimal (e.g. 10772:1985:1024:45::1
for 2a14:7c1:400:2d::1), which made request_id logs unreadable.

lib/microwaveprop_web/plugs/remote_ip.ex

@@ -173,7 +173,12 @@ defmodule MicrowavepropWeb.Plugs.RemoteIp do
       (e <<< 48) + (f <<< 32) + (g <<< 16) + h
   end
 
-  defp format_ip({a, b, c, d}), do: "#{a}.#{b}.#{c}.#{d}"
+  defp format_ip(ip) when tuple_size(ip) in [4, 8] do
-  defp format_ip({a, b, c, d, e, f, g, h}), do: "#{a}:#{b}:#{c}:#{d}:#{e}:#{f}:#{g}:#{h}"
+    case :inet.ntoa(ip) do
+      {:error, _} -> "unknown"
+      charlist -> List.to_string(charlist)
+    end
+  end
+
   defp format_ip(_), do: "unknown"
 end

test/microwaveprop_web/plugs/remote_ip_test.exs

@@ -249,6 +249,22 @@ defmodule MicrowavepropWeb.Plugs.RemoteIpTest do
       assert conn.remote_ip == {127, 0, 0, 1}
     end
 
+    test "logs IPv6 peer in canonical hex form, not decimal" do
+      # Regression: a public IPv6 client like 2a14:7c1:400:2d::1 was being
+      # logged as "10772:1985:1024:45:0:0:0:1" because we stringified the
+      # 8-tuple in decimal. Logger metadata should hold the canonical hex.
+      peer = {0x2A14, 0x07C1, 0x0400, 0x002D, 0, 0, 0, 1}
+
+      :get
+      |> conn("/")
+      |> with_peer(peer)
+      |> call_plug()
+
+      assert {:remote_ip, ip_str} = List.keyfind(Logger.metadata(), :remote_ip, 0)
+      assert ip_str =~ "2a14"
+      refute ip_str =~ "10772"
+    end
+
     test "single-host CIDR (/32) trusts only that exact IP" do
       conn =
         :get