feat: add client availability tracking and error handling improvements

- Introduced `IsAvailable` and `SetUnavailable` methods to clients for availability tracking.
- Integrated availability checks in client selection logic to skip unavailable clients.
- Enhanced error handling by marking clients unavailable on specific error codes (e.g., 401, 402).
- Removed redundant quota verification logs in client reordering logic.

internal/api/handlers/claude/code_handlers.go

@@ -205,9 +205,13 @@ outLoop:
 						err := cliClient.RefreshTokens(cliCtx)
 						if err != nil {
 							log.Debugf("refresh token failed, switch client, %s", util.HideAPIKey(cliClient.GetEmail()))
+							cliClient.SetUnavailable()
 						}
 						retryCount++
 						continue outLoop
+					case 402:
+						cliClient.SetUnavailable()
+						continue outLoop
 					default:
 						// Forward other errors directly to the client
 						c.Status(errInfo.StatusCode)