fix: prevent double date formatting in email templates

- Remove pre-formatting of dates before passing to email processor
- Let email processor handle all date formatting based on recipient language
- Fix Invalid Date errors by passing raw date values instead of formatted strings
- Remove unused formatDate imports and variables

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

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

backend/src/routes/adminEmail.js

@@ -210,15 +210,15 @@ router.get('/templates', adminAuth, async (req, res) => {
         id: template.id,
         template_key: template.template_key,
         variables: (() => {
-        try {
-          if (!template.variables) return [];
-          if (typeof template.variables === 'object') return template.variables;
-          return JSON.parse(template.variables);
-        } catch (e) {
-          console.warn('Failed to parse variables for template:', template.template_key, e.message);
-          return [];
-        }
-      })(),
+          try {
+            if (!template.variables) return [];
+            if (typeof template.variables === 'object') return template.variables;
+            return JSON.parse(template.variables);
+          } catch (e) {
+            console.warn('Failed to parse variables for template:', template.template_key, e.message);
+            return [];
+          }
+        })(),
         updated_at: template.updated_at
       };