fix(chat): isolate concurrent session events by refactoring WebSocket event handling (#365)

Refactored the WebSocket event handling mechanism to use global listeners with session-specific event routing instead of per-session listeners. This prevents event cross-talk when multiple chat sessions run concurrently.

Key changes:
- Client: Added sessionEventHandlers Map to route events to appropriate sessions
- Client: Registered global listeners once per socket connection
- Server: Extracted message processing logic into handleMessage method
- Server: Improved Hermes session ID tracking with dedicated Map
- Server: Added replaceByHermesSessionId for targeted message replacement

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/server/src/db/hermes/session-store.ts

@@ -421,6 +421,7 @@ export function updateSessionStats(id: string): void {
          last_active = COALESCE((SELECT MAX(timestamp) FROM ${MESSAGES_TABLE} WHERE session_id = ?), started_at)
      WHERE id = ?`,
   ).run(id, id, id)
+  console.log(`Updated session ${id} stats`)
 }
 
 export function getSessionDetailPaginated(