feat: add loading animation

public/loading/loading.css

+#preloadingAnimation{position:fixed;left:0;top:0;height:100%;width:100%;background:#ffffff;user-select:none;z-index: 9999;overflow: hidden}.lds-roller{display:inline-block;position:relative;left:50%;top:50%;transform:translate(-50%,-50%);width:64px;height:64px;}.lds-roller div{animation:lds-roller 1.2s cubic-bezier(0.5,0,0.5,1) infinite;transform-origin:32px 32px;}.lds-roller div:after{content:" ";display:block;position:absolute;width:6px;height:6px;border-radius:50%;background:#13c2c2;margin:-3px 0 0 -3px;}.lds-roller div:nth-child(1){animation-delay:-0.036s;}.lds-roller div:nth-child(1):after{top:50px;left:50px;}.lds-roller div:nth-child(2){animation-delay:-0.072s;}.lds-roller div:nth-child(2):after{top:54px;left:45px;}.lds-roller div:nth-child(3){animation-delay:-0.108s;}.lds-roller div:nth-child(3):after{top:57px;left:39px;}.lds-roller div:nth-child(4){animation-delay:-0.144s;}.lds-roller div:nth-child(4):after{top:58px;left:32px;}.lds-roller div:nth-child(5){animation-delay:-0.18s;}.lds-roller div:nth-child(5):after{top:57px;left:25px;}.lds-roller div:nth-child(6){animation-delay:-0.216s;}.lds-roller div:nth-child(6):after{top:54px;left:19px;}.lds-roller div:nth-child(7){animation-delay:-0.252s;}.lds-roller div:nth-child(7):after{top:50px;left:14px;}.lds-roller div:nth-child(8){animation-delay:-0.288s;}.lds-roller div:nth-child(8):after{top:45px;left:10px;}#preloadingAnimation .load-tips{color: #13c2c2;font-size:2rem;position:absolute;left:50%;top:50%;transform:translate(-50%,-50%);margin-top:80px;text-align:center;width:400px;height:64px;}  @keyframes lds-roller{0%{transform:rotate(0deg);} 100%{transform:rotate(360deg);}}
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public/loading/loading.html

+<div id="preloadingAnimation"><div class=lds-roller><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div></div><div class=load-tips>Loading</div></div>
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