Fixed Streamlit startup without API keys

[mounacheikho-cmd]

Summary

• Removed unused lingua-language-detector dependency
• Allowed Streamlit to start when API keys are missing
• Added clearer Settings guidance for missing or placeholder API keys
• Reinitialized the analyzer after a key is entered

Tests

• python -m pytest tests/test_api_key_manager.py tests/test_streamlit_app_basic.py tests/test_analyzer.py::test_document_analyzer_starts_without_api_keys -q

[suung]

Hey @mounacheikho-cmd - really cool work.
I left a few comments after our discussion before it's not clear for me if we still have the your-api-key "hacks" in there or if it works without them when the keys are just empty and the env.example is updated...

Pls let me know if you conclude we should keep it like that.

[suung]

Great work, only MINOR: the comment wether we still need the tests checking for keys with your- can be checked