feat: 足迹 Footprints 个人留痕系统

桌面应用(Tauri+React+SQLite)：时间线/记录/学年学科成绩梯度/统计/类型与字段模板/附件内容寻址/详情视图/PWA

同步服务端(sync-server)：多用户+邀请码/LWW推拉/seq游标/附件去重/Docker部署

多端同步地基：uuid v7/HLC混合逻辑时钟/软删除墓碑/sync_oplog，Node与Rust双端一致并通过自动化测试

app/src/components/ui/select.tsx

@@ -0,0 +1,28 @@
+import { forwardRef, type SelectHTMLAttributes } from 'react';
+import { ChevronDown } from 'lucide-react';
+import { cn } from '@/lib/utils';
+
+export interface Option { value: string; label: string; }
+
+export const Select = forwardRef<HTMLSelectElement, SelectHTMLAttributes<HTMLSelectElement> & { options?: Option[] }>(
+  function Select({ className, options, children, ...props }, ref) {
+    return (
+      <div className={cn('relative', className ? className.split(' ').filter(c => /^w-|^min-w|^flex-/.test(c)).join(' ') : '')}>
+        <select
+          ref={ref}
+          className={cn(
+            'w-full h-8 appearance-none rounded-md border border-line bg-surface pl-2.5 pr-7 text-[13px] text-ink-1',
+            'transition-colors hover:border-line-strong focus:border-brand focus:outline-none disabled:opacity-50',
+            className
+          )}
+          {...props}
+        >
+          {options
+            ? options.map(o => <option key={o.value} value={o.value}>{o.label}</option>)
+            : children}
+        </select>
+        <ChevronDown size={14} className="pointer-events-none absolute right-2 top-1/2 -translate-y-1/2 text-ink-3" />
+      </div>
+    );
+  }
+);