fix(i18n): Beschreibung-generieren-Button + Fehler-Toasts uebersetzbar

- Button-Span enhance-btn-text bekommt data-i18n.
- app.js: Loading-State Wird generiert... / Generating... per T().
- Vier Fehler-Toasts (Default, 503, 429, 504) per T() lokalisiert.
- Neue Keys enhance.* in de.json + en.json.
- Cache-Buster app.js auf v=20260513c gebumpt.

src/static/i18n/en.json

@@ -21,6 +21,11 @@
   "modal.new_incident.title_field": "Incident title",
   "modal.new_incident.description": "Description / context",
   "modal.new_incident.enhance": "Generate description",
+  "modal.new_incident.enhance_loading": "Generating...",
+  "enhance.error_default": "Description could not be generated",
+  "enhance.error_unavailable": "AI access currently unavailable. Please contact your administrator.",
+  "enhance.error_busy": "AI is currently busy. Please wait briefly and try again.",
+  "enhance.error_timeout": "AI is not responding. Please try again.",
   "modal.new_incident.visibility": "Visibility",
   "modal.new_incident.visibility_public": "Public",
   "modal.new_incident.visibility_private": "Private",