fix: improve stability with memory leak fixes and atomic writes

Session Manager:
- Store event handlers for proper cleanup on session stop
- Add resetSessionManager() for test isolation

State Store:
- Use atomic write pattern (temp file + rename) to prevent corruption
- Add tokenStats to AppState interface

Subagent Watcher:
- Clean up pendingToolCalls on agent completion
- Add cleanupStaleAgents() for 24h+ old agents
- Clear all state maps on stop() for clean restart

Web Server:
- Remove listeners from transcript watcher before stopping
- Clean up respawn timers when session is deleted
- Use cleanupSession() in spawn orchestrator for proper resource cleanup

Frontend:
- Close existing EventSource before reconnecting to prevent duplicates
- Close failed connection before scheduling reconnect

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/web/public/app.js

@@ -965,11 +965,22 @@ class ClaudemanApp {
   // ========== SSE Connection ==========
 
   connectSSE() {
+    // Close existing EventSource before creating new one to prevent duplicate connections
+    if (this.eventSource) {
+      this.eventSource.close();
+      this.eventSource = null;
+    }
+
     this.eventSource = new EventSource('/api/events');
 
     this.eventSource.onopen = () => this.setConnectionStatus('connected');
     this.eventSource.onerror = () => {
       this.setConnectionStatus('disconnected');
+      // Close the failed connection before scheduling reconnect
+      if (this.eventSource) {
+        this.eventSource.close();
+        this.eventSource = null;
+      }
       setTimeout(() => this.connectSSE(), 3000);
     };