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/machine.h

@@ -87,6 +87,11 @@ public:
     input_sources_t m_sources {};
     std::string m_result {};
     std::vector<Katom> m_katoms {};
+    // False on the sub-Machine that re-reads an @eval result (Eval::eval):
+    // result text is machine-generated -- a renderer's raw target markup
+    // (e.g. a LaTeX column spec "@{}...") legitimately fails katom parsing
+    // and must not produce "Word not parsed" warnings.
+    bool m_warn_unparsed = true;
 };
 
 /*