feat: Add language support to reports and frontend input

[hurxxxx]

This PR introduces support for specifying the language of generated reports by adding a language parameter. The default value is set to "english", ensuring backward compatibility while enabling multi-language support.

Changes

Backend

• Added language parameter to BasicReport and DetailedReport classes
• Updated GPTResearcher to store language in the Config object for use in report generation
• Modified server_utils.py and websocket_manager.py to extract and pass the language parameter

Frontend

• Added a new input field for selecting the report language (index.html, scripts.js)
• Ensured the selected language is sent to the backend when starting the report generation

Review

• Verified that the language parameter is correctly propagated from frontend → server → backend → GPTResearcher
• Maintained backward compatibility by defaulting to "english"
• Followed existing patterns in the codebase for consistency