feat(tree): complete rust family runtime checklist

- add tree shell runtime artifact contracts and page/filetree/picker runtime reducers
- sink tree.subtree.move write operation through Rust and formalize command event plans
- harden file tree search projection contract and route thin-proxy boundaries
- record completed harness tasks and move design docs into process/done

rust/crates/mnote-web/src/tree_shell/picker_renderer.rs

@@ -52,11 +52,12 @@ fn render_picker_row(
     children_by_parent: &BTreeMap<Option<String>, Vec<PickerRenderRow>>,
 ) {
     html.push_str(&format!(
-        r#"<li class="tree-node" data-node-id="{node_id}"><button type="button" class="tree-row" role="treeitem" aria-level="{aria_level}" aria-expanded="{expanded_attr}" data-rust-rendered-row="picker" data-testid="tree-picker-row" data-node-id="{node_id}" data-shell-mode="picker" data-focused="{active}" data-rust-action="pick"><span class="tree-spacer" aria-hidden="true"></span><span class="tree-kind-badge" data-kind="page" aria-hidden="true"></span><span class="tree-link"><span class="tree-link-title">{title}</span></span></button>"#,
+        r#"<li class="tree-node" data-node-id="{node_id}"><button type="button" class="tree-row" role="treeitem" aria-level="{aria_level}" aria-expanded="{expanded_attr}" data-rust-rendered-row="picker" data-testid="tree-picker-row" data-node-id="{node_id}" data-shell-mode="picker" data-focused="{active}" data-rust-action="pick" tabindex="{tabindex}"><span class="tree-spacer" aria-hidden="true"></span><span class="tree-kind-badge" data-kind="page" aria-hidden="true"></span><span class="tree-link"><span class="tree-link-title">{title}</span></span></button>"#,
         node_id = escape_html(&row.node_id),
         aria_level = row.depth + 1,
         expanded_attr = if row.expandable && row.expanded { "true" } else { "false" },
         active = row.active,
+        tabindex = if row.active { "0" } else { "-1" },
         title = escape_html(&row.title),
     ));
     if row.expandable && row.expanded {
@@ -77,8 +78,9 @@ pub fn render_initial_picker_html(input: &PickerInitialRenderInput) -> String {
     );
     if input.allow_root_pick {
         html.push_str(&format!(
-            r#"<li class="tree-node" data-node-id="__root__"><button type="button" class="tree-row" data-testid="tree-picker-root" data-rust-rendered-row="picker-root" data-rust-action="pick-root" data-focused="{focused}"><span class="tree-spacer" aria-hidden="true"></span><span class="tree-link"><span class="tree-link-title">根目录</span></span></button></li>"#,
+            r#"<li class="tree-node" data-node-id="__root__"><button type="button" class="tree-row" data-testid="tree-picker-root" data-rust-rendered-row="picker-root" data-rust-action="pick-root" data-focused="{focused}" tabindex="{tabindex}"><span class="tree-spacer" aria-hidden="true"></span><span class="tree-link"><span class="tree-link-title">根目录</span></span></button></li>"#,
             focused = input.root_active,
+            tabindex = if input.root_active { "0" } else { "-1" },
         ));
     }
 
@@ -180,6 +182,14 @@ mod tests {
                 expandable: false,
                 expanded: false,
                 active: true,
+            }, PickerRenderRow {
+                node_id: "page_other".into(),
+                parent_node_id: None,
+                title: "其他页面".into(),
+                depth: 0,
+                expandable: false,
+                expanded: false,
+                active: false,
             }],
         });
 
@@ -190,5 +200,7 @@ mod tests {
         assert!(html.contains("data-testid=\"tree-picker-row\""));
         assert!(html.contains("首页 &lt;安全&gt;"));
         assert!(html.contains("data-focused=\"true\""));
+        assert!(html.contains("tabindex=\"0\""));
+        assert!(html.contains("tabindex=\"-1\""));
     }
 }