feat(web): session list one-list, hover card, row menus, rename, manual ordering

Sidebar session list grows the figma 239-10458 feature set and the
workspace/session browsing region moves wholesale into ui-workspace:

- Group-by menu (WorkSpace / In one list): flat mode lists every session
  top-level, strictly newest-first; the choice persists across reloads.
- Session rows get a 500ms hover detail card (title / relative time /
  status line) and a ... menu (Rename / Fork session / Delete session,
  visual-only for now); workspace headers get ... with Rename (wired) and
  Delete workspace (visual-only).
- workspace.rename RPC: trims, rejects duplicate titles on the create
  chain (workspace-name-conflict), no-op on same title; modal dialog with
  client-side duplicate pre-check.
- workspace.insertSessionBefore RPC (DOM-insertBefore semantics, omitted
  anchor appends): HTML5 drag reorder of root sessions inside a workspace
  group; order truth stays host-side, the view refreshes from the
  response/changed frame.
- Activity pinning removed: the session/event touchSession chain is gone;
  workspace accounts are manually owned (new sessions prepend, explicit
  reordering only). Contracts and tests updated, api catalog regenerated.
- ui-sidebar reduced to the column shell (brand, fold state machine, New
  Session, Settings) exposing one sidebar.workspaces hole with a two-fact
  owner share {wide, expandSidebar}; ui-workspace owns the whole region
  (header, search, grouped/flat lists, dialogs, drag) plus the picker via
  a shared WorkspaceCreateFlow. The old sidebar.workspace picker slot and
  its deferral indirection are gone.
- ui-primitives: Menu gains label entries, danger rows, and
  closeOnPointerLeave; new HoverCard (portaled, open-delay, disabled
  guard). Hover card and row menu never coexist.

packages/client/ui-primitives/src/Menu.module.css

@@ -109,6 +109,27 @@
   background: transparent;
 }
 
+/* Destructive row: error text/icon, danger hover fill. */
+.danger {
+  color: var(--dsw-alias-state-error-primary);
+}
+
+.danger .itemIcon {
+  color: var(--dsw-alias-state-error-primary);
+}
+
+.danger:hover:not(:disabled) {
+  background: var(--dsw-alias-interactive-bg-hover-danger);
+}
+
+/* Heading row: non-interactive small grey text, padding aligned with items. */
+.label {
+  padding: 8px 10px;
+  font-size: 12px;
+  line-height: 16px;
+  color: var(--dsw-alias-label-tertiary);
+}
+
 /* Separator cell (figma 122:9481): py 4 / px 2 around the hairline. */
 .separator {
   height: 1px;