Add support for a web translator service

As a translator, I would like automatically generated translations of a whole file from the engineering language to the target language.
Proposed workflow:

• user loads TS file in Qt Linguist
• user triggers automatic translation of the whole file via menu item
• dialog opens where the user can choose translation service, enter the API key, select whether to overwrite existing unfinished translations, ...
• all unfinished translations get populated with automatic translations. These translations stay in 'unfinished' state.
• user reviews the unfinished translations manually

Additionally, we could offer a separate action for auto-translating the currently opened message.

If AI services (Claude, ChatGPT, local ollama...) are used then

• consider using MCP for connecting to these services
• consider offering a separate text field to enter a preface prompt to give the LLM more context about the nature of the messages ("This is a medical application UI used for minimal invasive surgery...")