fix: division-by-zero guard, rate-limit wallet endpoints, safer JSON parse, Lighter HTTP checks

- Guard GridCount-1 division by zero in grid spacing calculation (both grid.go and grid_levels.go)
- Rate-limit /wallet/validate and /wallet/generate endpoints (prevent DoS on key generation)
- Wrap JSON.parse(localStorage) in try-catch in AuthContext (corrupted data → graceful re-login)
- Wrap handleJSONResponse JSON.parse in try-catch with descriptive error
- Add HTTP status code checks for Lighter GetActiveOrders and sendTx
- Replace deprecated strings.Title with cases.Title (golang.org/x/text)
- Reuse HTTP client in checkClaw402Health (was creating new client per call)

trader/lighter/orders.go

@@ -246,6 +246,14 @@ func (t *LighterTraderV2) GetActiveOrders(symbol string) ([]OrderResponse, error
 		return nil, fmt.Errorf("failed to read response: %w", err)
 	}
 
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		snippet := string(body)
+		if len(snippet) > 512 {
+			snippet = snippet[:512] + "..."
+		}
+		return nil, fmt.Errorf("GetActiveOrders API HTTP error (status %d): %s", resp.StatusCode, snippet)
+	}
+
 	logger.Debugf("📋 LIGHTER GetActiveOrders raw response: %s", string(body))
 
 	// Parse response - Lighter API uses "orders" field, not "data"

trader/lighter/trading.go

@@ -394,6 +394,14 @@ func (t *LighterTraderV2) submitOrder(txType int, txInfo string) (map[string]int
 		return nil, err
 	}
 
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		snippet := string(respBody)
+		if len(snippet) > 512 {
+			snippet = snippet[:512] + "..."
+		}
+		return nil, fmt.Errorf("Lighter sendTx HTTP error (status %d): %s", resp.StatusCode, snippet)
+	}
+
 	// Parse response
 	var sendResp SendTxResponse
 	if err := json.Unmarshal(respBody, &sendResp); err != nil {