fix: Broken /terms and /privacy routes (#749)

* fix: replace invalid redirect("about:blank") with proper controller actions

The privacy and terms routes were using redirect("about:blank") which is
invalid because about:blank is a browser-specific pseudo URL, not a valid
HTTP redirect target. This fix replaces them with proper controller actions
that render placeholder pages.

Changes:
- Add privacy and terms actions to PagesController with skip_authentication
- Create privacy.html.erb and terms.html.erb view templates
- Add i18n translations for the new pages
- Update routes to use pages#privacy and pages#terms

https://claude.ai/code/session_01RL36dMda1o6LXGsnGnTJZu

* Make legal routes configurable

---------

Co-authored-by: Claude <noreply@anthropic.com>

app/controllers/pages_controller.rb

@@ -1,7 +1,7 @@
 class PagesController < ApplicationController
   include Periodable
 
-  skip_authentication only: :redis_configuration_error
+  skip_authentication only: %i[redis_configuration_error privacy terms]
 
   def dashboard
     @balance_sheet = Current.family.balance_sheet
@@ -55,6 +55,14 @@ class PagesController < ApplicationController
     render layout: "blank"
   end
 
+  def privacy
+    render layout: "blank"
+  end
+
+  def terms
+    render layout: "blank"
+  end
+
   private
     def preferences_params
       prefs = params.require(:preferences)