feat: AI cost tracking, pre-launch balance check, low balance alerts

- store/ai_charge.go: local AI cost tracking per call (SQLite)
- wallet/usdc.go: shared USDC balance query (Base chain RPC)
- Pre-launch: estimate daily cost + runway days
- Low balance: warn <$1, error at $0 (every 10 cycles)
- API: GET /api/ai-costs for cost history
- Frontend: model cards show price per call
- Frontend: wallet create + QR deposit + balance display

store/store.go

@@ -28,6 +28,7 @@ type Store struct {
 	equity         *EquityStore
 	order          *OrderStore
 	grid           *GridStore
+	aiCharge       *AIChargeStore
 	telegramConfig TelegramConfigStore
 
 	mu sync.RWMutex
@@ -160,6 +161,9 @@ func (s *Store) initTables() error {
 	if err := s.TelegramConfig().(*telegramConfigStore).initTables(); err != nil {
 		return fmt.Errorf("failed to initialize telegram config tables: %w", err)
 	}
+	if err := s.AICharge().initTables(); err != nil {
+		return fmt.Errorf("failed to initialize AI charge tables: %w", err)
+	}
 	return nil
 }
 
@@ -283,6 +287,16 @@ func (s *Store) Grid() *GridStore {
 	return s.grid
 }
 
+// AICharge gets AI charge storage
+func (s *Store) AICharge() *AIChargeStore {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.aiCharge == nil {
+		s.aiCharge = NewAIChargeStore(s.gdb)
+	}
+	return s.aiCharge
+}
+
 // TelegramConfig gets Telegram bot configuration storage
 func (s *Store) TelegramConfig() TelegramConfigStore {
 	s.mu.Lock()