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>

sks/kutil/kutil.k

@@ -69,3 +69,14 @@ An <id> is the value of the ^:id argument for an image.
 
 ^:pattern before(?^:\s+\d+)?^|after(?^:\s+\d+)?^|[-\w]+
 @@@
+
+@@@argtype filename_list |
+  one or more filenames.  Filenames may contain spaces: a list is separated
+  by a standalone "/" (whitespace on both sides), e.g.
+  "chapter 1.kt / chapter 2.kt".  Without the separator, the names are
+  separated by whitespace, and names that do not exist are rejoined with
+  their neighbors into names that do.  A leading ~ expands to the home
+  directory.
+  :pattern [\s\S]*
+  :python_cast (lambda s: __import__("kutil").filename_list(s))
+@@@

sks/kutil/kutil.py

@@ -219,3 +219,37 @@ def format_for_paragraphs(s):
     return result
 
 
+
+def filename_list(text):
+    """Split a filename list; the Python twin of resolve_filename_list()
+    in mac/file.cpp (keep the two in sync).  A standalone "/" (whitespace
+    on both sides) separates names, whose inner spacing is preserved;
+    without a separator, whitespace-separated tokens that do not name
+    existing files are rejoined with their neighbors into names that do.
+    A leading ~ expands to the home directory."""
+    text = text.strip()
+    if not text:
+        return []
+    parts = re.split(r'(?:^|(?<=\s))/(?:\s|$)', text)
+    if len(parts) > 1:
+        return [os.path.expanduser(p.strip()) for p in parts if p.strip()]
+    tokens = text.split()
+    result, i = [], 0
+    while i < len(tokens):
+        if os.path.isfile(os.path.expanduser(tokens[i])):
+            result.append(tokens[i])
+            i += 1
+            continue
+        acc, j, found = tokens[i], i + 1, False
+        while j < len(tokens):
+            acc += " " + tokens[j]
+            j += 1
+            if os.path.isfile(os.path.expanduser(acc)):
+                result.append(acc)
+                i = j
+                found = True
+                break
+        if not found:
+            result.append(tokens[i])
+            i += 1
+    return [os.path.expanduser(p) for p in result]