Add exclamation mark to RSVP CTA button ("I'm attending!")

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

frontend/src/components/__tests__/RsvpBar.spec.ts

@@ -6,7 +6,7 @@ describe('RsvpBar', () => {
   it('renders CTA button when hasRsvp is false', () => {
     const wrapper = mount(RsvpBar)
     expect(wrapper.find('.rsvp-bar__cta').exists()).toBe(true)
-    expect(wrapper.find('.rsvp-bar__cta-inner').text()).toBe("I'm attending")
+    expect(wrapper.find('.rsvp-bar__cta-inner').text()).toBe("I'm attending!")
     expect(wrapper.find('.rsvp-bar__status').exists()).toBe(false)
   })