fix(projects): scope email rollup to CRM types + re-render unstored previews

- The customer address often doubles as the admin notification target, so
  matching emails purely by recipient swept in system alerts (backup_failed,
  restore_failed, …). The recipient match is now restricted to CRM document
  types (quote_/contract_/invoice_/storno_); event-scoped mails still match
  by event_id.
- getEmailPreview now falls back to renderQueuedEmail() — re-rendering from
  the current template + the row's stored email_data — for emails sent before
  rendered_html capture, flagged exact:false with an amber 're-rendered' note.
  Only a missing template / no variables falls through to 'nothing stored'.

Known limitation: a customer with multiple projects sees their event_id=null
CRM mails under each (email_queue has no project_id).

frontend/src/i18n/locales/de.json

@@ -3439,7 +3439,8 @@
       "cancel": "Abbrechen",
       "retry": "Wiederholen",
       "previewTitle": "E-Mail-Vorschau",
-      "noPreview": "Keine gespeicherte Vorschau für diese E-Mail — sie wurde gesendet, bevor Vorschauen erfasst wurden."
+      "noPreview": "Keine gespeicherte Vorschau für diese E-Mail — sie wurde gesendet, bevor Vorschauen erfasst wurden.",
+      "reRendered": "Neu gerendert aus der aktuellen Vorlage — diese E-Mail wurde gesendet, bevor Vorschauen erfasst wurden, und kann daher leicht von der tatsächlich versendeten abweichen."
     },
     "toast": {
       "created": "Projekt erstellt",

frontend/src/i18n/locales/en.json

@@ -3439,7 +3439,8 @@
       "cancel": "Cancel",
       "retry": "Retry",
       "previewTitle": "Email preview",
-      "noPreview": "No stored preview for this email — it was sent before previews were captured."
+      "noPreview": "No stored preview for this email — it was sent before previews were captured.",
+      "reRendered": "Re-rendered from the current template — this email was sent before previews were captured, so it may differ slightly from what the recipient received."
     },
     "toast": {
       "created": "Project created",

frontend/src/pages/admin/projects/ProjectCockpitPage.tsx

@@ -404,7 +404,14 @@ export const ProjectCockpitPage: React.FC = () => {
               {previewLoading ? (
                 <Loading />
               ) : preview && preview.available && preview.html ? (
-                <iframe title="email-preview" srcDoc={preview.html} className="w-full h-[60vh] border border-neutral-200 dark:border-neutral-700 rounded bg-white" />
+                <>
+                  {!preview.exact && (
+                    <div className="mb-3 rounded-md bg-amber-50 dark:bg-amber-900/30 border border-amber-200 dark:border-amber-800 px-3 py-2 text-xs text-amber-800 dark:text-amber-200">
+                      {t('projects.email.reRendered', 'Re-rendered from the current template — this email was sent before previews were captured, so it may differ slightly from what the recipient received.')}
+                    </div>
+                  )}
+                  <iframe title="email-preview" srcDoc={preview.html} className="w-full h-[60vh] border border-neutral-200 dark:border-neutral-700 rounded bg-white" />
+                </>
               ) : (
                 <div className="text-center py-10 text-neutral-500">
                   {t('projects.email.noPreview', 'No stored preview for this email — it was sent before previews were captured.')}

frontend/src/services/projects.service.ts

@@ -118,6 +118,9 @@ export interface EmailPreview {
   type: string;
   status: string;
   available: boolean;
+  /** true = exact bytes stored at send time; false = re-rendered from the
+   *  current template (approximation for emails sent before capture). */
+  exact: boolean;
   html: string | null;
 }