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>

tst/Makefile

@@ -1,9 +1,10 @@
 # Klammertext distribution test suite (subset).
 #
-# Runs the three shell regression suites:
-#   cond_test.sh    — @cond argument delimitation
-#   deftype_test.sh — the four klammer definition modes + redefinition table
-#   escape_test.sh  — target character escaping and quoted specials
+# Runs the four shell regression suites:
+#   cond_test.sh     — @cond argument delimitation
+#   deftype_test.sh  — the four klammer definition modes + redefinition table
+#   escape_test.sh   — target character escaping and quoted specials
+#   filename_test.sh — filenames with spaces (quoting, " / " lists, rescue)
 #
 # Requires KLAMMERTEXT_HOME set and `ktext` on PATH (build it with `make -C com`).
 
@@ -12,3 +13,4 @@ test:
 	./cond_test.sh
 	./deftype_test.sh
 	./escape_test.sh
+	./filename_test.sh