feat: 头像上传选区限制 3840×3840 + 客户端裁剪压缩

- 后端：3840×2160 限制改为 3840×3840（方形限制适应方形裁剪），并移到裁剪结果上检查而非原图
- 前端：原图短边超过 3840 时自动抬高最小缩放，确保选区永不超过 3840×3840
- 前端：裁剪确认后用 Canvas 预裁剪 + JPEG 压缩再上传，大幅节省带宽
- 前端：裁剪框标题栏新增实时像素尺寸提示
- 新增 .crop-info 样式

internal/service/avatar_service.go

@@ -26,7 +26,7 @@ const (
 	avatarMinWidth    = 128                 // 最小宽高，防止马赛克图被拉升
 	avatarMinHeight   = 128
 	avatarMaxWidth    = 3840
-	avatarMaxHeight   = 2160
+	avatarMaxHeight   = 3840
 	avatarOutputSize  = 512
 	avatarTargetKB    = 100
 	avatarStorageDir  = "storage/uploads/avatars"
@@ -98,9 +98,7 @@ func (s *AvatarService) ProcessImage(userID uint, file io.Reader, contentType st
 	}
 	bounds := img.Bounds()
 	w, h := bounds.Dx(), bounds.Dy()
-	if w > avatarMaxWidth || h > avatarMaxHeight {
+	// 原图只检查最小尺寸，确保有足够像素供上采样
-		return "", fmt.Errorf("图片分辨率不能超过 3840x2160")
-	}
 	if w < avatarMinWidth || h < avatarMinHeight {
 		return "", fmt.Errorf("图片分辨率不能低于 128x128")
 	}
@@ -114,6 +112,13 @@ func (s *AvatarService) ProcessImage(userID uint, file io.Reader, contentType st
 		cropped = centerCrop(img)
 	}
 
+	// 裁切后检查最大尺寸（用户实际选区不应超过此限制）
+	cb := cropped.Bounds()
+	cw, ch := cb.Dx(), cb.Dy()
+	if cw > avatarMaxWidth || ch > avatarMaxHeight {
+		return "", fmt.Errorf("裁切区域分辨率不能超过 3840x3840")
+	}
+
 	// 5. 缩放至 512x512（CatmullRom 高质量）
 	resized := image.NewNRGBA(image.Rect(0, 0, avatarOutputSize, avatarOutputSize))
 	draw.CatmullRom.Scale(resized, resized.Bounds(), cropped, cropped.Bounds(), draw.Over, nil)

templates/MetaLab-2026/html/settings/index.html

@@ -238,7 +238,7 @@
 <!-- 头像裁切弹窗 -->
 <div class="crop-overlay" id="cropOverlay">
     <div class="crop-dialog">
-        <div class="crop-header">调整裁切范围</div>
+        <div class="crop-header">调整裁切范围 <span class="crop-info" id="cropInfo"></span></div>
         <div class="crop-stage" id="cropStage">
             <img id="cropImageEl" draggable="false">
             <div class="crop-mask" id="cropMask"></div>
@@ -376,9 +376,11 @@
     var pendingFile = null;
     var imgNW, imgNH;       // 原图像素尺寸
     var imgDW, imgDH;       // 图片缩放后显示尺寸（zoom=1 基准）
-    var zoom = 1;           // 图片缩放系数 1.0 ~ 3.0
+    var zoom = 1;           // 图片缩放系数
+    var minZoom = 1;        // 最小缩放系数（超大图限制选区不超过 3840px）
     var panX = 0, panY = 0; // 图片平移偏移量
     var fSize, fLeft, fTop; // 裁切框的固定屏幕像素：边长、左、顶
+    var CROP_MAX_PX = 3840; // 选区最大像素限制
 
     // 更新裁切框固定参数（图片加载时计算一次，之后不变）
     function initFrame() {
@@ -418,6 +420,11 @@
         cropMask.style.top    = fTop + 'px';
         cropMask.style.width  = fSize + 'px';
         cropMask.style.height = fSize + 'px';
+
+        // 实时显示选区像素尺寸
+        var p = getCropParams();
+        var infoEl = document.getElementById('cropInfo');
+        if (infoEl) infoEl.textContent = p.size + ' × ' + p.size + ' px';
     }
 
     function openCrop(file) {
@@ -431,7 +438,11 @@
                 var fit = Math.min(sw / imgNW, sh / imgNH);
                 imgDW = Math.round(imgNW * fit);
                 imgDH = Math.round(imgNH * fit);
-                zoom = 1;
+                // 限制选框最大像素：原图短边超过 3840 时，抬高最小缩放
+                minZoom = Math.min(imgNW, imgNH) > CROP_MAX_PX
+                    ? Math.min(imgNW, imgNH) / CROP_MAX_PX
+                    : 1;
+                zoom = minZoom;
                 panX = 0;
                 panY = 0;
                 initFrame();
@@ -514,7 +525,7 @@
     cropStage.addEventListener('wheel', function (e) {
         e.preventDefault();
         if (panning) return;
-        var newZoom = Math.max(1, Math.min(zoom * (e.deltaY < 0 ? 1.1 : 1 / 1.1), 3));
+        var newZoom = Math.max(minZoom, Math.min(zoom * (e.deltaY < 0 ? 1.1 : 1 / 1.1), 3));
         if (newZoom === zoom) return;
         zoom = newZoom;
         clampPan();
@@ -526,19 +537,52 @@
         if (e.target === cropOverlay) closeCrop();
     });
 
+    // 客户端裁剪 + 压缩：用 Canvas 裁出选区，转 JPEG 后上传，大幅节省带宽
+    function cropOnClient(file, x, y, size) {
+        return new Promise(function (resolve) {
+            var url = URL.createObjectURL(file);
+            var img = new Image();
+            img.onload = function () {
+                URL.revokeObjectURL(url);
+                var out = Math.min(size, 2048);  // 不超过 2048px，避免 Canvas 内存过大
+                var canvas = document.createElement('canvas');
+                canvas.width = out;
+                canvas.height = out;
+                var ctx = canvas.getContext('2d');
+                ctx.drawImage(img, x, y, size, size, 0, 0, out, out);
+                canvas.toBlob(function (blob) {
+                    resolve({
+                        file: new File([blob], 'avatar.jpg', { type: blob.type || 'image/jpeg' }),
+                        cropX: 0,
+                        cropY: 0,
+                        cropSize: out
+                    });
+                }, 'image/jpeg', 0.88);
+            };
+            img.onerror = function () {
+                URL.revokeObjectURL(url);
+                // Canvas 处理失败时回退：直接上传原文件 + 原坐标
+                resolve({ file: file, cropX: x, cropY: y, cropSize: size });
+            };
+            img.src = url;
+        });
+    }
+
     cropConfirmBtn.addEventListener('click', function () {
         if (!pendingFile) return;
         var params = getCropParams();
-        var formData = new FormData();
-        formData.append('avatar', pendingFile);
-        formData.append('crop_x', params.x);
-        formData.append('crop_y', params.y);
-        formData.append('crop_size', params.size);
 
         cropConfirmBtn.disabled = true;
         cropConfirmBtn.textContent = '处理中...';
         showSettingsToast('上传中...');
 
+        cropOnClient(pendingFile, params.x, params.y, params.size).then(function (result) {
+            var formData = new FormData();
+            formData.append('avatar', result.file, result.file.name);
+            formData.append('crop_x', result.cropX);
+            formData.append('crop_y', result.cropY);
+            formData.append('crop_size', result.cropSize);
+
             var xhr = new XMLHttpRequest();
             xhr.open('POST', '/api/settings/avatar', true);
             xhr.onreadystatechange = function () {
@@ -562,6 +606,11 @@
                 }
             };
             xhr.send(formData);
+        }).catch(function () {
+            cropConfirmBtn.disabled = false;
+            cropConfirmBtn.textContent = '确认';
+            showSettingsToast('处理失败，请重试', true);
+        });
     });
 
     if (avatarWrap && avatarInput) {

templates/MetaLab-2026/static/css/settings.css

@@ -362,6 +362,13 @@ body {
     border-bottom: 1px solid var(--color-border);
 }
 
+.crop-info {
+    font-size: .75rem;
+    color: var(--color-text-secondary);
+    font-weight: 400;
+    margin-left: .5rem;
+}
+
 .crop-stage {
     position: relative;
     width: min(85vw, 480px);