Filenames with spaces; output beside the input file; warning fixes (from dev c08eb1bbfa4c)

- Filenames may contain spaces: quote on the command line; filename
  lists use a standalone "/" separator; unseparated names that do not
  exist are rejoined into names that do (announced); leading ~ expands.
- Without -o, output is written to the input file's directory; -o fully
  specifies the output directory and basename.
- "Word not parsed" warnings now appear without -v, only for text that
  survives removal, with correct line numbers.
- New tst/filename_test.sh regression suite.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

mac/eval.cpp

@@ -158,6 +158,7 @@ katom_list Eval::eval(katom_iter begin, katom_iter end)
     std::string eval_result = eval_command(begin, end);
     katom_list result {};
     Machine M = m_machine;
+    M.m_warn_unparsed = false; // Result text is machine-generated (see machine.h)
     size_t before = M.m_katoms.size();
     M.read(eval_result);
     // If the @eval produced more Klammertext -- the read-back result still