feat: persistent token tracking with global stats aggregation

- Add restoreTokens() method to Session class for recovery after restart
- Add GlobalStats type for cumulative usage tracking across all sessions
- Accumulate tokens from deleted sessions into global stats
- Track lifetime session count with incrementSessionsCreated()
- Add /api/stats endpoint for global stats
- Include globalStats in /api/status response
- Frontend shows aggregate tokens + cost in header
- Fix respawn controller config to filter undefined values
- Add 7 new tests for global stats functionality (v0.1343)

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

src/session.ts

@@ -571,6 +571,16 @@ export class Session extends EventEmitter {
     return this._totalOutputTokens;
   }
 
+  /**
+   * Restore token and cost values from saved state.
+   * Called when recovering sessions after server restart.
+   */
+  restoreTokens(inputTokens: number, outputTokens: number, totalCost: number): void {
+    this._totalInputTokens = inputTokens;
+    this._totalOutputTokens = outputTokens;
+    this._totalCost = totalCost;
+  }
+
   get autoClearThreshold(): number {
     return this._autoClearThreshold;
   }