Phase 1 (#4662): address Codex + Opus gate findings

Codex (CORE regression): the parallelized loadDir('.') started BEFORE the
_switchGen stale-switch guard; empty-session switches reuse the session id, so a
superseded switch's /api/list could paint the wrong profile's tree. Reverted to
guard-before-workspace-render ordering (the up-front skeletons already give the
immediate cross-surface feedback; the parallel gain was marginal).

Opus findings:
- [blocker] Workspace skeleton stranded permanently when the new profile has no
  bound workspace (loadDir skipped → nothing clears #fileTree). Added
  clearWorkspaceTreeSkeleton() (only empties when a skeleton is present) and call
  it on the no-workspace path in BOTH switch branches.
- [low-med] Session-list skeleton stranded if an inline-rename input or row
  action menu was open (renderSessionListFromCache early-returns before the DOM
  swap). Dismiss _renamingSid + closeSessionActionMenu() before showing the
  skeleton.
- [low] No-op self-switch flashed skeleton→restore (activateCurrentProfile
  doesn't pre-check). Added an early-return when name === S.activeProfile.

Tests: +4 static assertions for the self-switch guard, rename/menu dismissal,
no-workspace skeleton clear, and the clear-helper definition. 22 pass.

static/workspace.js

@@ -475,6 +475,18 @@ function showWorkspaceTreeSkeleton(){
   tree.style.display = '';
 }
 
+// Clear a stranded workspace-tree skeleton (#4662 Opus gate). showWorkspaceTreeSkeleton()
+// is shown up front on a profile switch, but the real loadDir('.') that would
+// replace it is skipped when the new profile has no bound workspace — leaving a
+// shimmering skeleton forever. Call this on the no-workspace path so the tree
+// empties instead. Only touches #fileTree when it still holds a skeleton, so
+// it can't clobber a real render.
+function clearWorkspaceTreeSkeleton(){
+  const tree = $('fileTree');
+  if(!tree) return;
+  if(tree.querySelector('.skeleton-tree')) tree.innerHTML = '';
+}
+
 async function loadDir(path, opts={}){
   const preservePreview=!!(opts&&opts.preservePreview);
   const refreshExpanded=!!(opts&&opts.refreshExpanded);