feat: implement email unsubscribe page

- Create /email/unsubscribe/[id] route with page and component
- Add share-id validation and 404 on invalid links
- Add bilingual translations (English/Croatian)
- Implement unsubscribe UI with success/error states
- Call unsubscribeTenantEmail server action on button click

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

web-app/messages/en.json

@@ -446,6 +446,33 @@
       "unknown": "An error occurred during verification. Please try again or contact your landlord."
     }
   },
+  "email-unsubscribe-page": {
+    "title": "Unsubscribe from Email Notifications",
+    "about": {
+      "title": "About Evidencija Režija",
+      "description": "Evidencija Režija is a utility bills tracking application that helps landlords manage their properties and notify tenants about rent and utility bills."
+    },
+    "why": {
+      "title": "Why are you receiving emails?",
+      "description": "Your landlord has configured the application to send rent due and/or utility bills notifications to your email address."
+    },
+    "what-happens": {
+      "title": "What happens after unsubscribing?",
+      "description": "After you unsubscribe, you will no longer receive any rent due or utility bill notifications via email. Your landlord will need to contact you through other means."
+    },
+    "button": {
+      "unsubscribe": "Confirm Unsubscribe",
+      "unsubscribing": "Unsubscribing..."
+    },
+    "success": {
+      "title": "Successfully Unsubscribed",
+      "message": "You have been unsubscribed from email notifications. You will no longer receive rent or utility bill reminders."
+    },
+    "error": {
+      "title": "Unsubscribe Failed",
+      "unknown": "An error occurred while unsubscribing. Please try again or contact your landlord."
+    }
+  },
   "privacy-policy-page": {
     "title": "Privacy Policy for the Utility Bill Tracking Web App",
     "meta": {