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/ko.json

@@ -274,6 +274,9 @@
         "civitaiApiKey": "Civitai API 키",
         "civitaiApiKeyPlaceholder": "Civitai API 키를 입력하세요",
         "civitaiApiKeyHelp": "Civitai에서 모델을 다운로드할 때 인증에 사용됩니다",
+        "civitaiApiKeyConfigured": "설정됨",
+        "civitaiApiKeyNotConfigured": "설정되지 않음",
+        "civitaiApiKeySet": "설정",
         "civitaiHost": {
             "label": "Civitai 호스트",
             "help": "\"View on Civitai\" 링크를 사용할 때 어떤 Civitai 사이트를 열지 선택합니다.",