fix(auth): 修复移动端短信登录图形验证码挤占输入框空间

input 改为 flex:1 1 0% + width:0 强制占据剩余空间，图形验证码按钮固定
78px 并用 overflow:hidden 拘住 SVG 固有尺寸，避免被 132px 图片撑开
导致输入框被挤到 32px 宽

frontend/src/features/auth/views/MobileLoginView.vue

@@ -318,7 +318,8 @@ async function handlePasswordLogin() {
 }
 
 .auth-input-row input {
-  flex: 1;
+  flex: 1 1 0%;
+  width: 0;
   min-width: 0;
   border: none;
   padding: 14px 16px;
@@ -339,8 +340,10 @@ async function handlePasswordLogin() {
 .captcha-image-button {
   display: grid;
   place-items: center;
-  min-width: 110px;
-  height: 44px;
+  flex: 0 0 78px;
+  width: 78px;
+  height: 38px;
+  margin: 2px 6px 2px 0;
   border: none;
   border-radius: 8px;
   background: #fff7ed;
@@ -359,8 +362,9 @@ async function handlePasswordLogin() {
 
 .captcha-image-button img {
   display: block;
-  width: 110px;
-  height: 44px;
+  width: 100%;
+  height: 100%;
+  object-fit: cover;
 }
 
 .code-row {
@@ -368,13 +372,14 @@ async function handlePasswordLogin() {
 }
 
 .code-action {
-  min-width: 110px;
+  flex: 0 0 auto;
+  min-width: 92px;
   padding: 4px;
 }
 
 .code-btn {
   width: 100%;
-  font-size: 12px !important;
+  font-size: 11px !important;
 }
 
 .assist-row {