fix(directory): read recursive flag as mrb_bool to prevent unintended recursive delete

[ratazzi]

Problem

mrb_get_args format b writes a single mrb_bool (u8), but recursive_val was declared as mrb_value (8 bytes, undefined-initialized). mrb_test() then read the 7 uninitialized high bytes, so the flag evaluated as true regardless of what the Ruby DSL passed.

A plain

directory "/some/dir" do
  action :delete
end

(recursive defaults to false) could therefore recursively delete the whole subtree instead of failing on a non-empty directory — silent data loss.

This is the same b-format pitfall previously fixed in macos_dock.zig; this call site was missed.

Fix

Declare the variable as mruby.mrb_bool and compare against zero, matching the existing pattern in remote_file.zig. Swept the repo for other b format specifiers paired with mrb_value — this was the only remaining one.

Testing

Verified end to end with the built binary:

• Non-recursive action :delete on a non-empty directory now fails with DirNotEmpty and leaves the tree intact (previously deleted it).
• recursive true still deletes the tree.
• zig build test passes.