feat(goals/new): standalone page render when not in a Turbo frame

Direct nav to /goals/new used to render the index page with an empty
modal frame because the entire template was wrapped in DS::Dialog.
The URL was effectively un-shareable.

Branch on turbo_frame_request? — Turbo Frame requests still render
the DS::Dialog wrapper (the existing in-modal flow on the index page
keeps working). Non-frame requests render a standalone page-level
header (h1 + subtitle + icon) followed by the form_stepper partial.
Same Stimulus controller, same data-goal-stepper-modal-subtitle
selector, so the stepper's subtitle update path works identically.

Controller sets @breadcrumbs so the standalone variant gets the
Home > Goals > New goal trail.

Verified both paths via Playwright: direct GET renders standalone
form with h1 "New goal" + no dialog; click-from-index opens the
DS::Dialog with the stepper inside.

app/controllers/goals_controller.rb

@@ -45,6 +45,11 @@ class GoalsController < ApplicationController
       currency: Current.family.primary_currency_code
     )
     @linkable_accounts = linkable_accounts_for_new
+    @breadcrumbs = [
+      [ t("breadcrumbs.home"), root_path ],
+      [ t("goals.index.title"), goals_path ],
+      [ t("goals.new.heading"), nil ]
+    ]
   end
 
   def create