fix(ionosphere): disable TLS verify for GIRO to unbreak ionosonde fetch

lgdc.uml.edu's TLS handshake doesn't include the InCommon RSA Server
CA 2 intermediate, and Erlang/OTP's chain decode trips on an ASN.1
table-constraint mismatch even when the intermediate is merged into
the trust store. The data is public, read-only, unauthenticated
ionosonde measurements, so verify_none is scoped to this one client
rather than let the pipeline stay dark.

lib/microwaveprop/ionosphere/giro_client.ex

@@ -56,7 +56,7 @@ defmodule Microwaveprop.Ionosphere.GiroClient do
     Microwaveprop.Instrument.span([:giro, :fetch], %{station: ursi_code}, fn ->
       url = build_url(ursi_code, from_dt, to_dt)
 
-      case Req.get(url, [receive_timeout: @default_timeout_ms] ++ req_options()) do
+      case Req.get(url, [receive_timeout: @default_timeout_ms] ++ merged_req_options()) do
         {:ok, %{status: 200, body: body}} when is_binary(body) ->
           parse_tabular(body)
 
@@ -192,4 +192,27 @@ defmodule Microwaveprop.Ionosphere.GiroClient do
   defp req_options do
     Application.get_env(:microwaveprop, :giro_req_options, [])
   end
+
+  # lgdc.uml.edu doesn't bundle the "InCommon RSA Server CA 2"
+  # intermediate in its handshake. Adding the intermediate to our trust
+  # store moves the error from unknown_ca to an Erlang/OTP asn1 table
+  # constraint mismatch during chain decode — :ssl trips on an
+  # extension shape it doesn't accept. Scope verify_none here is
+  # acceptable: GIRO data is public, read-only, unauthenticated
+  # ionosonde measurements, and the endpoint has no alternative. When
+  # the test config overrides :giro_req_options with a Req.Test plug,
+  # that override wins — :plug short-circuits before any TLS work, so
+  # verify_none never runs in tests.
+  defp merged_req_options do
+    case req_options() do
+      [] -> default_req_options()
+      overrides -> overrides
+    end
+  end
+
+  @doc false
+  @spec default_req_options() :: keyword()
+  def default_req_options do
+    [connect_options: [transport_opts: [verify: :verify_none]]]
+  end
 end

test/microwaveprop/ionosphere/giro_client_test.exs

@@ -66,4 +66,24 @@ defmodule Microwaveprop.Ionosphere.GiroClientTest do
       assert row.valid_time == ~U[2026-04-15 18:07:30Z]
     end
   end
+
+  describe "default_req_options/0" do
+    # lgdc.uml.edu's server doesn't bundle the "InCommon RSA Server CA 2"
+    # intermediate, and Erlang/OTP's chain-build path trips over an
+    # ASN.1 table-constraint mismatch even when the intermediate is
+    # merged into cacerts. The data is public read-only ionosonde
+    # measurements, so we accept verify_none for this specific endpoint
+    # rather than keep the pipeline dark. Scope is limited to the GIRO
+    # client — other HTTPS callers still verify normally.
+    test "returns transport_opts with verify disabled for the GIRO endpoint" do
+      opts = GiroClient.default_req_options()
+
+      transport_opts =
+        opts
+        |> Keyword.fetch!(:connect_options)
+        |> Keyword.fetch!(:transport_opts)
+
+      assert Keyword.get(transport_opts, :verify) == :verify_none
+    end
+  end
 end