feat(spaceshd): pinned workspace field

Add a `pinned` bool to the workspace model, threaded through proto
(Workspace + WorkspaceView + SetWorkspaceMeta), the registry, the
set_workspace_meta handler, persistence, the CLI mapping, and the Tauri
bridge. serde(default) keeps existing state.json compatible (pinned=false).
Backs the sidebar Favorites section.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/spaceshd/src/server.rs

@@ -461,12 +461,13 @@ async fn handle_request(
             let _ = out.send(ok(id, serde_json::Value::Null)).await;
         }
 
-        Cmd::SetWorkspaceMeta { workspace_id, name, group_id, unread, order } => {
+        Cmd::SetWorkspaceMeta { workspace_id, name, group_id, unread, order, pinned } => {
             let found = reg.workspace_mut(&workspace_id).map(|w| {
                 if let Some(n) = name { w.name = n; }
                 if let Some(g) = group_id { w.group_id = g; }
                 if let Some(u) = unread { w.unread = u; }
                 if let Some(o) = order { w.order = o; }
+                if let Some(p) = pinned { w.pinned = p; }
             }).is_some();
             if found {
                 if let Some(view) = reg.workspace_view(&workspace_id) {