fix(chat): use ~/.codex/skills/ for Codex expert symlinks and keep expert button always enabled

Change Codex skill storage to use only ~/.codex/skills/ instead of
~/.agents/skills/, and never disable the expert skills button so users
can always access the empty-state hint. Also fix stale expert list in
conversation window after linking in the separate settings window by
re-fetching on window focus.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src-tauri/src/commands/experts.rs

@@ -851,9 +851,8 @@ pub async fn experts_unlink_from_agent(
 
     let _guard = mutation_lock().lock().await;
 
-    // Scan ALL global dirs for this agent to handle shared-dir agents
-    // (Codex and Cline both point at `~/.agents/skills/`). Remove the
-    // link wherever it is found.
+    // Scan ALL global dirs for this agent to handle shared-dir agents.
+    // Remove the link wherever it is found.
     let dirs = scoped_skill_dirs(agent_type, AgentSkillScope::Global, None)
         .map_err(|_| ExpertsError::UnsupportedAgent(agent_type))?;