feat(import): confirm column mapping in a preview before importing members

lib/mv_web/live/import_live.ex

@@ -99,7 +99,12 @@ defmodule MvWeb.ImportLive do
           <.form_section title={gettext("Choose CSV file")}>
             <Components.custom_fields_notice {assigns} />
             <Components.template_links {assigns} />
-            <Components.import_form {assigns} />
+            <%= if @import_status != :preview do %>
+              <Components.import_form {assigns} />
+            <% end %>
+            <%= if @import_status == :preview do %>
+              <Components.preview {assigns} />
+            <% end %>
             <%= if @import_status == :running or @import_status == :done or @import_status == :error do %>
               <Components.import_progress {assigns} />
             <% end %>
@@ -133,6 +138,29 @@ defmodule MvWeb.ImportLive do
     end
   end
 
+  @impl true
+  def handle_event("confirm_import", _params, socket) do
+    case socket.assigns do
+      %{import_state: import_state} when is_map(import_state) ->
+        start_import(socket, import_state)
+
+      _ ->
+        {:noreply,
+         put_flash(socket, :error, gettext("No prepared import to confirm. Please upload again."))}
+    end
+  end
+
+  @impl true
+  def handle_event("cancel_import", _params, socket) do
+    socket =
+      socket
+      |> assign(:import_state, nil)
+      |> assign(:import_progress, nil)
+      |> assign(:import_status, :idle)
+
+    {:noreply, socket}
+  end
+
   # Checks if all prerequisites for starting an import are met.
   #
   # Validates:
@@ -169,10 +197,10 @@ defmodule MvWeb.ImportLive do
     end
   end
 
-  # Processes CSV upload and starts import process.
+  # Processes CSV upload and enters the mapping preview.
   #
-  # Reads the uploaded CSV file, prepares it for import, and initiates
-  # the chunked processing workflow.
+  # Reads the uploaded CSV file and prepares it (read-only at the DB level), then
+  # shows the mapping preview. No member is created until the user confirms.
   @spec process_csv_upload(Phoenix.LiveView.Socket.t()) ::
           {:noreply, Phoenix.LiveView.Socket.t()}
   defp process_csv_upload(socket) do
@@ -181,7 +209,7 @@ defmodule MvWeb.ImportLive do
     with {:ok, content} <- consume_and_read_csv(socket),
          {:ok, import_state} <-
            MemberCSV.prepare(content, max_rows: Config.csv_import_max_rows(), actor: actor) do
-      start_import(socket, import_state)
+      enter_preview(socket, import_state)
     else
       {:error, reason} when is_binary(reason) ->
         {:noreply,
@@ -193,6 +221,19 @@ defmodule MvWeb.ImportLive do
     end
   end
 
+  # Shows the mapping preview without starting any processing.
+  @spec enter_preview(Phoenix.LiveView.Socket.t(), map()) ::
+          {:noreply, Phoenix.LiveView.Socket.t()}
+  defp enter_preview(socket, import_state) do
+    socket =
+      socket
+      |> assign(:import_state, import_state)
+      |> assign(:import_progress, nil)
+      |> assign(:import_status, :preview)
+
+    {:noreply, socket}
+  end
+
   # Starts the import process by initializing progress tracking and scheduling the first chunk.
   @spec start_import(Phoenix.LiveView.Socket.t(), map()) ::
           {:noreply, Phoenix.LiveView.Socket.t()}
@@ -263,7 +304,9 @@ defmodule MvWeb.ImportLive do
       custom_field_lookup: import_state.custom_field_lookup,
       existing_error_count: length(progress.errors),
       max_errors: @max_errors,
-      actor: actor
+      actor: actor,
+      fee_type_map: import_state.fee_type_map,
+      groups_found: import_state.groups_found
     ]
 
     _ =