phsl / new-api

* Added a dedicated effect to merge origin and selected models, ensuring selected items always remain in the dropdown list.
* Enhanced “Copy all models” button:
  * Shows info message when list is empty.
  * Displays success / error notification based on copy result.
* Unified UI look-and-feel by applying `!rounded-lg` class to inputs, selects, banners and buttons.
* i18n: added English translations for new prompts
  - "No models to copy"
  - "Model list copied to clipboard"
  - "Copy failed"