♻️ refactor(lsp_server): move entrypoints out of named modules

- export Run() from launcher module and add non-module main TU
- apply same pattern to module-based test executables
- migrate utils/string implementation fully into string.cppm and drop string.cpp
- point clangd to linux build compilation database

lsp-server/test/test_ast/test.cppm

@@ -120,7 +120,7 @@ void PrintUsage(const char* program_name)
     std::cout << "  " << program_name << " test.tsf -s -n  # Show source without colors\n";
 }
 
-int main(int argc, char* argv[])
+export int Run(int argc, char* argv[])
 {
     if (argc < 2)
     {