feat: 工作空间文件预览改为侧边栏内嵌面板

- 将文件预览从模态弹窗改为侧边栏内嵌面板，不打断用户操作流程
- 支持双拖动调整：外部调整整体宽度（400-800px），内部调整文件树宽度（180-300px）
- 左右分栏布局：左侧文件树 + 右侧预览面板
- 对话区域保留最小宽度 480px，保证可用性
- 新建 FilePreviewPanel 组件，删除 FilePreviewModal 组件
- 更新相关样式和规格文档

src/styles/components/workspace/_index.scss

@@ -4,14 +4,16 @@
 
 // 工作空间侧边栏
 .workspace-sidebar {
-    width: 240px;
+    width: 500px;
+    min-width: 400px;
+    max-width: 800px;
     background: var(--color-bg-2);
     border-left: 1px solid var(--color-border-2);
     display: flex;
     flex-direction: column;
     height: 100%;
     flex-shrink: 0;
-    transition: width 0.3s ease, opacity 0.3s ease;
+    transition: width 0.3s ease;
     position: relative;
 
     &--collapsed {
@@ -119,11 +121,57 @@
         }
     }
 
+    // ========== Content - 左右分栏 ==========
     &__content {
         flex: 1;
+        display: flex;
+        overflow: hidden;
+        min-height: 0;
+    }
+
+    // ========== FileTree ==========
+    &__file-tree {
+        min-width: 180px;
+        max-width: 300px;
+        flex-shrink: 0;
         overflow-y: auto;
         padding: 8px;
-        min-height: 0;
+        background: var(--color-bg-2);
+    }
+
+    // ========== 分隔线（可拖动） ==========
+    &__divider {
+        width: 1px;
+        background: var(--color-border-2);
+        flex-shrink: 0;
+        cursor: ew-resize;
+        position: relative;
+        transition: background 0.2s;
+
+        // 增加可拖动区域
+        &::before {
+            content: '';
+            position: absolute;
+            top: 0;
+            left: -4px;
+            right: -4px;
+            bottom: 0;
+            cursor: ew-resize;
+        }
+
+        &:hover {
+            background: var(--color-primary);
+        }
+    }
+
+    // ========== Preview Panel ==========
+    &__preview {
+        flex: 1;
+        min-width: 200px;
+        display: flex;
+        flex-direction: column;
+        overflow: hidden;
+        background: var(--color-bg-1);
     }
 
     &__resize-handle {
@@ -366,6 +414,144 @@
     }
 }
 
+// ========== 文件预览面板 ==========
+.file-preview-panel {
+    display: flex;
+    flex-direction: column;
+    height: 100%;
+    overflow: hidden;
+
+    // Header
+    &__header {
+        display: flex;
+        align-items: center;
+        padding: 12px 16px;
+        border-bottom: 1px solid var(--color-border-2);
+        gap: 8px;
+        flex-shrink: 0;
+        background: var(--color-bg-2);
+    }
+
+    &__icon {
+        font-size: 20px;
+        flex-shrink: 0;
+    }
+
+    &__name {
+        flex: 1;
+        font-size: 14px;
+        font-weight: 600;
+        color: var(--color-text-1);
+        overflow: hidden;
+        text-overflow: ellipsis;
+        white-space: nowrap;
+    }
+
+    &__close {
+        width: 24px;
+        height: 24px;
+        display: flex;
+        align-items: center;
+        justify-content: center;
+        border-radius: var(--radius-sm);
+        cursor: pointer;
+        color: var(--color-text-3);
+        transition: all 0.2s;
+        flex-shrink: 0;
+
+        &:hover {
+            background: var(--color-bg-1);
+            color: var(--color-text-1);
+        }
+    }
+
+    // Info
+    &__info {
+        padding: 12px 16px;
+        background: var(--color-bg-2);
+        border-bottom: 1px solid var(--color-border-2);
+        flex-shrink: 0;
+    }
+
+    &__info-item {
+        display: flex;
+        font-size: 13px;
+        margin-bottom: 6px;
+
+        &:last-child {
+            margin-bottom: 0;
+        }
+
+        .label {
+            width: 60px;
+            color: var(--color-text-3);
+            flex-shrink: 0;
+        }
+
+        .value {
+            flex: 1;
+            color: var(--color-text-1);
+        }
+    }
+
+    // Content Wrapper
+    &__content-wrapper {
+        flex: 1;
+        overflow-y: auto;
+        min-height: 0;
+    }
+
+    // Content
+    &__content {
+        padding: 16px;
+    }
+
+    &__code {
+        font-family: 'Courier New', Courier, monospace;
+        font-size: 13px;
+        line-height: 1.6;
+        color: var(--color-text-1);
+        white-space: pre-wrap;
+        word-break: break-all;
+        background: var(--color-bg-2);
+        padding: 12px;
+        border-radius: var(--radius-sm);
+        margin: 0;
+    }
+
+    // Placeholder
+    &__placeholder {
+        display: flex;
+        flex-direction: column;
+        align-items: center;
+        justify-content: center;
+        padding: 32px 16px;
+        text-align: center;
+        color: var(--color-text-3);
+        min-height: 200px;
+    }
+
+    &__placeholder-icon {
+        font-size: 48px;
+        margin-bottom: 12px;
+        opacity: 0.5;
+    }
+
+    &__placeholder-text {
+        font-size: 13px;
+    }
+
+    // Actions
+    &__actions {
+        padding: 12px 16px;
+        border-top: 1px solid var(--color-border-2);
+        display: flex;
+        gap: 8px;
+        flex-shrink: 0;
+        background: var(--color-bg-2);
+    }
+}
+
 // 文件右键菜单
 .file-context-menu {
     position: absolute;

src/styles/layouts/_chat-layout.scss

@@ -245,6 +245,7 @@
     background: var(--color-bg-1);
     min-height: 0;
     overflow: hidden;
+    min-width: 480px;  // 保证对话区域最小宽度
 }
 
 .chat-content__messages,