feat(write): 保存按钮改用鼠尾草绿主色

write 页的「保存」主按钮原为石墨黑 bg-paper-primary，与 dashboard
「写文章」等主操作按钮颜色不一致。改为 bg-paper-accent 鼠尾草绿，
统一后台所有主操作按钮配色。hover 改用 brightness-110 + active
scale 与其它主按钮交互手感一致。禁用态(saving)保持 paper-tertiary 灰。

src/pages/admin/write.rs

@@ -811,7 +811,7 @@ fn write_editor(post_id: Option<i32>) -> Element {
                     class: if saving() {
                         "px-5 py-1.5 text-sm bg-[var(--color-paper-tertiary)] text-[var(--color-paper-secondary)] rounded-xl font-medium cursor-not-allowed"
                     } else {
-                        "px-5 py-1.5 text-sm bg-[var(--color-paper-primary)] text-[var(--color-paper-theme)] rounded-xl font-medium hover:opacity-90 transition-opacity cursor-pointer"
+                        "px-5 py-1.5 text-sm bg-[var(--color-paper-accent)] text-[var(--color-paper-theme)] rounded-xl font-medium hover:brightness-110 active:scale-[0.98] transition-all cursor-pointer"
                     },
                     disabled: saving(),
                     onclick: on_submit,