♻️ 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_symbol/test.cppm

@@ -1050,7 +1050,7 @@ void AnalyzeFile(const Options& options)
 
 // ==================== 主程序 ====================
 
-int main(int argc, char* argv[])
+export int Run(int argc, char* argv[])
 {
     Options options;