feat: real SSE streaming for agent chat + data cleanup on startup

SSE Streaming:
- Add POST /api/agent/chat/stream endpoint with real SSE streaming
- Agent.HandleMessageStream() streams final LLM response via onEvent callback
- Tool-calling rounds use non-streaming; tool status sent as 'tool' events
- Frontend uses ReadableStream API instead of fake word-by-word setTimeout
- SSE events: tool (tool execution), delta (text chunk), done (complete), error

Data Maintenance:
- Add cleanupOldData() on server startup (decisions >90d, equity >180d)
- Add CleanOldRecords to DecisionStore and EquityStore
- Add store-level logger for cleanup operations

Exchange Traders:
- Add GetAccountInfo() to Bitget, Bybit, Indodax, KuCoin, Lighter, OKX traders
- Remove unused imports in Aster/Lighter traders

store/decision.go

@@ -247,12 +247,16 @@ func (s *DecisionStore) GetRecordsByDate(traderID string, date time.Time) ([]*De
 	return records, nil
 }
 
-// CleanOldRecords cleans old records from N days ago
+// CleanOldRecords cleans old records from N days ago.
+// If traderID is empty, cleans records for ALL traders.
 func (s *DecisionStore) CleanOldRecords(traderID string, days int) (int64, error) {
 	cutoffTime := time.Now().AddDate(0, 0, -days)
 
-	result := s.db.Where("trader_id = ? AND timestamp < ?", traderID, cutoffTime).
-		Delete(&DecisionRecordDB{})
+	query := s.db.Where("timestamp < ?", cutoffTime)
+	if traderID != "" {
+		query = query.Where("trader_id = ?", traderID)
+	}
+	result := query.Delete(&DecisionRecordDB{})
 	if result.Error != nil {
 		return 0, fmt.Errorf("failed to clean old records: %w", result.Error)
 	}

store/equity.go

@@ -117,12 +117,16 @@ func (s *EquityStore) GetAllTradersLatest() (map[string]*EquitySnapshot, error)
 	return result, nil
 }
 
-// CleanOldRecords cleans old records from N days ago
+// CleanOldRecords cleans old records from N days ago.
+// If traderID is empty, cleans records for ALL traders.
 func (s *EquityStore) CleanOldRecords(traderID string, days int) (int64, error) {
 	cutoffTime := time.Now().AddDate(0, 0, -days)
 
-	result := s.db.Where("trader_id = ? AND timestamp < ?", traderID, cutoffTime).
-		Delete(&EquitySnapshot{})
+	query := s.db.Where("timestamp < ?", cutoffTime)
+	if traderID != "" {
+		query = query.Where("trader_id = ?", traderID)
+	}
+	result := query.Delete(&EquitySnapshot{})
 	if result.Error != nil {
 		return 0, fmt.Errorf("failed to clean old records: %w", result.Error)
 	}