feat(settings): hide API key from frontend, use status+edit instead of password field

Backend changes:
- Add civitai_api_key to _NO_SYNC_KEYS, return only boolean civitai_api_key_set
- Clean up known template placeholder on load to prevent false positive

Frontend changes:
- Replace type=password with type=text + CSS masking (-webkit-text-security)
- Replace pre-filled input with status display (Configured/Not configured)
- Add inline edit view with Save/Cancel buttons
- Re-add eye toggle via CSS class toggle (not type switching)
- Use CSS transitions for smooth status/edit view switching

This prevents Chromium/Vivaldi password manager from triggering
'save password' prompts when opening the settings modal.

locales/de.json

@@ -274,6 +274,9 @@
         "civitaiApiKey": "Civitai API Key",
         "civitaiApiKeyPlaceholder": "Geben Sie Ihren Civitai API Key ein",
         "civitaiApiKeyHelp": "Wird für die Authentifizierung beim Herunterladen von Modellen von Civitai verwendet",
+        "civitaiApiKeyConfigured": "Konfiguriert",
+        "civitaiApiKeyNotConfigured": "Nicht konfiguriert",
+        "civitaiApiKeySet": "Einrichten",
         "civitaiHost": {
             "label": "Civitai-Host",
             "help": "Wählen Sie aus, welche Civitai-Seite geöffnet wird, wenn Sie „View on Civitai“-Links verwenden.",