vimPlugins.b4-review-vim: init at 0.15.2

b4's `misc/vim` directory provides ftdetect/ftplugin/syntax files that
highlight the `b4 review` reply editor (activating for *.b4-review.eml
buffers). Package them as a Vim/Neovim plugin, sourced from the b4
package's `passthru.src-misc` so the version stays in lockstep with b4
itself, following the notmuch-vim/hurl precedent.

Assisted-by: Claude Code (Claude Opus 4.8)

pkgs/applications/editors/vim/plugins/non-generated/b4-review-vim/default.nix

@@ -0,0 +1,19 @@
+{
+  lib,
+  vimUtils,
+  b4,
+}:
+vimUtils.buildVimPlugin {
+  pname = "b4-review-vim";
+  inherit (b4) version;
+
+  src = b4.src-misc;
+  sourceRoot = "${b4.src-misc.name}/misc/vim";
+
+  meta = {
+    description = "Vim syntax highlighting for the b4 review reply editor";
+    homepage = "https://git.kernel.org/pub/scm/utils/b4/b4.git/about";
+    license = lib.licenses.gpl2Only;
+    maintainers = with lib.maintainers; [ fzakaria ];
+  };
+}