docs(styles): explain toolbar inheritance and workspace layering

src/components/workspace/workspace.module.css

@@ -128,6 +128,7 @@
 .settingsActions button[type="submit"] { background: #37352f; color: white; border-color: #37352f; }
 .settingsActions button:disabled { opacity: 0.5; cursor: not-allowed; }
 /* 固定全视口画布置于底层；点阵背景与加载/错误状态由后续类分别承担。 */
+/* 主画布铺满整个视口，不按侧栏宽度缩窄；侧栏/浮动条通过更高层级叠在画布上方。 */
 .graph { position: fixed; inset: 0; z-index: 0; display: flex; width: 100%; height: 100dvh; background: #fffefb; }
 .graphSurface { width: 100%; height: 100%; background-image: radial-gradient(#b8aea245 1px, transparent 1px); background-size: 22px 22px; }
 .graphStatus { position: absolute; left: 50%; top: 72px; transform: translateX(-50%); max-width: calc(100vw - 48px); padding: 8px 12px; border-radius: 6px; background: #fffefbe6; color: #9a948c; text-align: center; font-size: 13px; }
@@ -173,4 +174,5 @@
 .directoryToggle { display: grid; place-items: center; border: 0; border-radius: 4px; background: transparent; color: #87837c; cursor: pointer; }
 .directoryToggle:hover { background: #eae7e2; }
 .directoryToggle:focus-visible { outline: 2px solid #9b877a; outline-offset: -2px; }
+/* 此处旋转过渡没有单独的 reduced-motion 覆盖；上面的媒体查询只关闭指定的菜单/浮动条效果。 */
 .directoryToggle svg { transition: transform 120ms ease; }