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>

config/locales/views/pages/en.yml

@@ -3,6 +3,14 @@ en:
   pages:
     changelog:
       title: What's new
+    privacy:
+      title: Privacy Policy
+      heading: Privacy Policy
+      placeholder: Privacy policy content will be displayed here.
+    terms:
+      title: Terms of Service
+      heading: Terms of Service
+      placeholder: Terms of service content will be displayed here.
     dashboard:
       welcome: "Welcome back, %{name}"
       subtitle: "Here's what's happening with your finances"