ludicc / ludic build: --stdin-file <path> checks an unsaved buffer in place of its file (R10)

stdin is read once, whole, and read_file serves a copy of it wherever the program opens <path> -
the entry, an import through a barrel, a component's .xml / .lss, an .lres. Paths match after
normalising both ('/' separators, relative under $PWD, . / .. / // folded, case on Windows);
diagnostics keep the file's usual name, with the buffer's lines and columns. A <path> nothing
opens is one warning. On ludic build it implies --check. Reseeded; bootstrap-cfree fixpoint holds.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/ludic-cli/main.ludic

@@ -48,6 +48,7 @@ program Ludic {
     print("                                compile to build/<name> (a native binary, nothing to ship beside it)")
     print("  build [file] --check          only check it: types, modules, uses and ports; nothing emitted")
     print("  build [file] --check --diagnostics=json   every error as a JSON array on stdout")
+    print("  build [file] --check --stdin-file PATH    stdin is PATH's unsaved text (an editor's buffer)")
     print("  test [file|dir...] [-j N] [-v] [--test NAME]")
     print("                                compile and run the project's tests (-v: every test's line)")
     print("  deps [file] [--graph|--dot|--writes|--uses MOD|--check F|--baseline F]")