fix(pdf-export): match DateTime.from_iso8601 three-tuple when formatting cells

DateTime.from_iso8601/1 returns {:ok, datetime, offset}, so the two-tuple clauses never matched and datetime cells fell through to the naive-parse fallback. Matching the real shape routes them through the intended DateTime path; UTC values render identically.

lib/mv/membership/members_pdf.ex

@@ -143,7 +143,7 @@ defmodule Mv.Membership.MembersPDF do
 
   defp convert_to_template_format(export_data, locale, club_name) do
     # Set locale for translations
-    Gettext.put_locale(MvWeb.Gettext, locale)
+    _ = Gettext.put_locale(MvWeb.Gettext, locale)
 
     headers = Enum.map(export_data.columns, & &1.label)
     column_count = length(export_data.columns)
@@ -211,9 +211,6 @@ defmodule Mv.Membership.MembersPDF do
       {:ok, datetime, _offset} ->
         format_datetime(datetime, locale)
 
-      {:ok, datetime} ->
-        format_datetime(datetime, locale)
-
       {:error, _} ->
         # Try NaiveDateTime if DateTime parsing fails
         case NaiveDateTime.from_iso8601(iso8601_string) do
@@ -257,8 +254,6 @@ defmodule Mv.Membership.MembersPDF do
     end
   end
 
-  defp format_date(_, _), do: ""
-
   defp format_dates_in_rows(rows, columns, locale) do
     date_indices = find_date_column_indices(columns)
 
@@ -321,7 +316,7 @@ defmodule Mv.Membership.MembersPDF do
 
   defp format_cell_date_datetime(cell_value, locale) do
     case DateTime.from_iso8601(cell_value) do
-      {:ok, datetime} -> format_datetime(datetime, locale)
+      {:ok, datetime, _offset} -> format_datetime(datetime, locale)
       _ -> format_cell_date_naive(cell_value, locale)
     end
   end

test/mv/membership/members_pdf_test.exs

@@ -101,6 +101,29 @@ defmodule Mv.Membership.MembersPDFTest do
       assert byte_size(pdf_binary) > 1000
     end
 
+    test "renders date column holding an ISO8601 datetime value" do
+      # Regression: a date column whose value is a full datetime string must be
+      # parsed via DateTime.from_iso8601/1 (which returns a 3-tuple) and rendered,
+      # not silently dropped.
+      export_data = %{
+        columns: [
+          %{key: "first_name", kind: :member_field, label: "Vorname"},
+          %{key: "join_date", kind: :member_field, label: "Eintritt"}
+        ],
+        rows: [
+          ["Max", "2024-01-15T14:30:00Z"]
+        ],
+        meta: %{
+          generated_at: "2024-01-15T14:30:00Z",
+          member_count: 1
+        }
+      }
+
+      assert {:ok, pdf_binary} = MembersPDF.render(export_data)
+      assert String.starts_with?(pdf_binary, "%PDF")
+      assert byte_size(pdf_binary) > 1000
+    end
+
     test "generates valid PDF with custom fields and computed fields" do
       export_data = %{
         columns: [