Fix LSP default language configuration

[sylvesterkaczmarek]

Fixes #393.

The LSP front-end settings had C as the active language globally but an empty basic-language map, causing textDocument/didOpen to fail in getBasicLang.

Provide the C basic-language settings used by the front end and make C the explicit default target language. This keeps the LSP independent of the code-generation backend while restoring the expected default configuration.

Validation:

• reproduced the KeyNotFoundException on current master with an LSP initialize/initialized/didOpen sequence
• repeated the same sequence after the fix and received textDocument/publishDiagnostics with no exception
• dotnet build lsp/Server/Server/Server.csproj -c Release passes on .NET 10

[sylvesterkaczmarek]

Thanks for merging this. Much appreciated.