chore(release): prepare 1.8.1 metadata and release contracts

Synchronize package versions and bilingual notes with verified issue references.
Allow releases without PR contributors to omit that section, with positive and
negative format coverage as requested by the maintainer.

Keep native update process operations and default-shell resolution inside the
platform boundary. Preserve transaction authority in the updater and tighten
the platform condition budget to the measured 484.

nebula_split/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "nebula-split"
-version = "1.8.0"
+version = "1.8.1"
 license = "GPL-3.0-or-later"
 description = "Shared split-pane rules: layout tree, geometry, divider drag and directional focus"
 publish = false