scm.sh ls-files: Honor -f in Git repositories

In CVS, the -f option keeps directory entries out of scm.sh ls-file's
listing; in Git, it's a silent no-op. Notably symlinks are not excluded
despite -f.

Implement -f for git with a mode filter on git ls-files -s output: only
100644 and 100755 entries are listed, so the option means the same thing in
both code paths.

For Git, this actually means a behaviour change which needs to be fixed:

The dist archive targets tar-files and cpio-files in make/list-files.mk and
the scm_files() helper in scripts/pkg.sh then may no longer pass it to get
unchanged behaviour.

The targets list-files and list-text-files keep it, so the text-files cache
now matches its documented regular-files-only membership.

Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v0.85.1
Signed-off-by: Jan Lindemann <jan@janware.com>

scripts/pkg.sh

@@ -101,7 +101,7 @@ scm_files()
 {
 	(
 		cd $TOPDIR
-		/bin/bash $JWB_SCRIPT_DIR/scm.sh ls-files -f "$@"
+		/bin/bash $JWB_SCRIPT_DIR/scm.sh ls-files "$@"
 	)
 }