feat: 收口本地文件夹入口并推进 page aggregate rust-first

- 为 Rust Web 主入口补齐本地文件夹/云空间切换、最近目录与路径回填体验\n- 对齐 local markdown media 与 inline marks 的 Rust shell / TipTap converter 语义\n- 让 documents/page 优先消费 Rust page aggregate snapshot，并保留 TS fallback\n- 补强 tree live、local markdown 与主入口 smoke，并同步设计稿状态

rust/crates/mnote-web/src/ssr/styles.rs

@@ -233,6 +233,7 @@ a:hover {
   gap: 10px;
   padding: 12px 16px 8px;
   justify-content: flex-start;
+  position: relative;
 }
 
 .wolai-avatar {
@@ -256,12 +257,75 @@ a:hover {
   font-weight: 650;
 }
 
+.mnote-workspace-source-trigger {
+  min-width: 0;
+  flex: 1 1 auto;
+  display: inline-flex;
+  align-items: center;
+  gap: 4px;
+  border: 0;
+  background: transparent;
+  padding: 2px 4px;
+  border-radius: 4px;
+  cursor: pointer;
+}
+
+.mnote-workspace-source-trigger:hover,
+.mnote-workspace-source-trigger[aria-expanded="true"] {
+  background: var(--wolai-bg-hover);
+}
+
 .wolai-sidebar-chevron {
   margin-left: auto;
   color: var(--wolai-text-secondary);
   font-size: 16px;
 }
 
+.mnote-workspace-source-menu {
+  position: absolute;
+  inset-inline-start: 0;
+  top: calc(100% + 6px);
+  z-index: 120;
+  width: 250px;
+  max-width: calc(100vw - 24px);
+  padding: 6px;
+  border: 1px solid rgba(27, 28, 28, 0.12);
+  border-radius: 8px;
+  background: #fff;
+  box-shadow: 0 16px 36px rgba(15, 23, 42, 0.18);
+}
+
+.mnote-workspace-source-menu__label {
+  padding: 8px 8px 4px;
+  color: var(--wolai-text-secondary);
+  font-size: 12px;
+}
+
+.mnote-workspace-source-menu__item {
+  width: 100%;
+  display: block;
+  border: 0;
+  border-radius: 6px;
+  background: transparent;
+  padding: 8px;
+  color: var(--wolai-text-primary);
+  font-size: 13px;
+  line-height: 1.35;
+  text-align: left;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  cursor: pointer;
+}
+
+.mnote-workspace-source-menu__item:hover {
+  background: var(--wolai-bg-hover);
+}
+
+.mnote-workspace-source-menu__item--primary {
+  color: #1D4ED8;
+}
+
 .wolai-quick-actions {
   flex: 0 0 auto;
   display: grid;