feat: support concurrent session streaming, persist active session, and improve 401 handling

- Refactor streaming to use Map<string, AbortController> for multi-session concurrency
- SSE callbacks capture session ID in closure, no cross-session interference
- messages is now computed from activeSession, no manual sync needed
- Persist active session ID to localStorage, restore on reload
- Auto-expand session group when restoring saved session
- Clear auth key and redirect to login on 401 (skip if already on login page)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "hermes-web-ui",
-  "version": "0.2.4",
+  "version": "0.2.5",
   "description": "Hermes Agent Web UI - Chat and Job Management Dashboard",
   "repository": {
     "type": "git",