Improve cart and dark mode UX

- Clear cart when customer logs out
- Hide cart bag button for non-authenticated users (only show for logged-in customers)
- Fix dark mode text visibility in all form inputs (input/textarea/select elements)

Addresses user request: cart should clear on logout and only be accessible to logged-in customers.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/app/globals.css

@@ -24,6 +24,11 @@
   body {
     @apply bg-paper text-ink font-body antialiased transition-colors duration-200;
   }
+  input,
+  textarea,
+  select {
+    @apply text-ink;
+  }
   ::selection {
     @apply bg-splash-pink text-paper;
   }