fix privacy policy niggles and add last-updated date to legal pages

- Capitalise lead sentence regardless of shop_name value
- Add stripe.com/privacy URL when mentioning Stripe in payment section
- Remove mention of logout from session cookie description
- Make third-party sharing text provider-agnostic (no longer names Printify etc.)
- Add :updated_at block to privacy, delivery, and terms pages showing when
  content last changed — auto-tracked via content hash, so the date advances
  automatically whenever relevant settings change

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

assets/css/shop/components.css

@@ -2043,10 +2043,16 @@
 
   .rich-text-lead {
     font-size: var(--t-text-large);
-    margin-bottom: 1rem;
+    margin-bottom: 0.5rem;
     color: var(--t-text-primary);
   }
 
+  .rich-text-updated-at {
+    font-size: var(--t-text-small);
+    color: var(--t-text-secondary);
+    margin-bottom: 2rem;
+  }
+
   .rich-text-paragraph {
     margin-bottom: 1rem;
     color: var(--t-text-secondary);