patch 9.1.1042: filetype: just files are not recognized

Problem:  filetype: just files are not recognized
Solution: adjust filetype detection pattern, detect just shebang line,
          include just ftplugin, indent and syntax plugin
          (Peter Benjamin)

closes: #16466

Signed-off-by: Peter Benjamin <petermbenjamin@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/ftplugin/just.vim b/runtime/ftplugin/just.vim
new file mode 100644
index 0000000..6f2acdd
--- /dev/null
+++ b/runtime/ftplugin/just.vim
@@ -0,0 +1,17 @@
+" Vim ftplugin file
+" Language:	Justfile
+" Maintainer:	Peter Benjamin <@pbnj>
+" Last Change:	2025 Jan 19
+" Credits:	The original author, Noah Bogart <https://github.com/NoahTheDuke/vim-just/>
+
+" Only do this when not done yet for this buffer
+if exists("b:did_ftplugin")
+  finish
+endif
+let b:did_ftplugin = 1
+
+setlocal iskeyword+=-
+setlocal comments=n:#
+setlocal commentstring=#\ %s
+
+let b:undo_ftplugin = "setlocal iskeyword< comments< commentstring<"