♻️ 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_lsp_any/test_main.cppm

@@ -10,7 +10,7 @@ import lsp.test.lsp_any.transformer;
 import lsp.test.lsp_any.facade;
 import lsp.test.lsp_any.common;
 
-int main()
+export int Run()
 {
     lsp::test::TestRunner runner;