fix setup flow stale state and Stripe URL issues

Onboarding: re-fetch setup_status() after provider/Stripe connect instead
of manually patching the local assigns, which could miss admin_created and
leave users stuck on the setup page with no way forward.

Dev config: respect PHX_HOST for endpoint URL so Stripe checkout redirects
to the correct host instead of always using localhost.

Stripe setup: detect private/LAN IPs (10.x, 172.16-31.x, 192.168.x) as
unreachable, not just localhost — prevents creating webhook endpoints that
Stripe can never reach.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/berrypod_web/live/setup/onboarding.ex

@@ -150,12 +150,7 @@ defmodule BerrypodWeb.Setup.Onboarding do
       case Products.create_provider_connection(params) do
         {:ok, connection} ->
           Products.enqueue_sync(connection)
-
-          setup = %{
-            socket.assigns.setup
-            | provider_connected: true,
-              provider_type: type
-          }
+          setup = Setup.setup_status()
 
           {:noreply,
            socket
@@ -183,14 +178,7 @@ defmodule BerrypodWeb.Setup.Onboarding do
 
       case StripeSetup.connect(api_key) do
         {:ok, _result} ->
-          setup = %{socket.assigns.setup | stripe_connected: true}
-
-          setup =
-            if setup.admin_created and setup.provider_connected do
-              %{setup | setup_complete: true}
-            else
-              setup
-            end
+          setup = Setup.setup_status()
 
           {:noreply,
            socket